I used to be a big Outlook user, finding it the only PIM client that kept my life even slightly sorted. I was so tied to Outlook that when I first brought my Intel based Mac, I quickly installed the beta release of Boot Camp, XP and got Outlook going. For the first couple of months of owning a Mac, I ran Windows almost exclusively.
Outlooks IMAP support has always been my single biggest peev. That, and its continued use of a single PST file for all data storage. There a lot of good reasons to not use a single file db, mainly if it corrupts you could loose ALL your previous history from emails to contacts. I have seen more than one person just about cry when they loose all their digital lives thanks to a Windows reinstall and not seeing their well hidden PST file deep in the documents & settings folders.

Of course Outlook being a Microsoft program, export options are nonexistent, unless you wanted to move to, say, Outlook. If so then no worries.
There are commercial applications that can take care of this whole process but I like to do things the free, slightly harder way – so for you all here is a compilation of various steps to take a large PST file to a complete export to iCal, Address Book and Mail.app (or other standard supporting applications on other platforms).
These steps are for Windows XP and Outlook 2007, but should be the same or very similar on Vista.

Getting your email to Mail.app.
This is originally from Schwie’s Pad’s blog post, refined by myself.

• First you’ll need a copy of Outlook Express installed on your XP machine. In our case we’re going to use it as a conversion tool and not the just the shittiest email client ever. I would recommend a virgin setup of Outlook Express.
• Open Outlook Express, it should detect your other Outlook profile and ask if you want to import the profile. If it doesn’t detect Outlook, you can import your mail manually. Under the File menu, choose Import, Messages. Choose Microsoft Outlook.
• Choose the default profile and then choose selected folders and choose any folders that have email in them. You can use CTRL to select multiple folders. You do not need to choose contacts or calendars, that is done via other workarounds below.
  
• It should spend sometime slurping through your emails and bringing them into Outlook Express.
• Once they are all imported, we now need to access the Outlook Express .dbx email files, these are stored in your Documents & Setting folder on your system drive (probably C:\). Best plan is to enable hidden files (via Tools menu, properties) and then go through the folders from C:\ – in my case it was – C:\Documents and Settings\Administrator\Local Settings\Application Data\Identities\{D54D6AEB-503D-49E3-BD59-11545746A4D2}\Microsoft\Outlook Express
  The two italicized names can be different but you should be able to get there.
• Now you’ll need a little command line app by Ulrich Krebs called DbxConv.exe. It’s freeware and available here. Extract the zip into you Outlook Express folder you just found. This program will convert your email folders from MS’s dbx format to the standard mbox format.
• Open command line via the Start Menu and Run command – from here type CMD.
• Now for the tricky bit, as command line was designed from the days of 8.3 file names theres no real easy way to get your way to a folder buried deep in windows file system – I have discovered though if you type “cd ” and then drag the folder icon in the address bar of explorer to the line in command line, it will insert the full folder address in to the  command. Press enter and you should be in the same folder as the files you need to convert.

• Now in command prompt type this command – dbxconv -mbx *.dbx
• Depending on the size of your original pst file it could take a while (up to 20mins). You will see few failed items that don’t convert (such as Contacts, calendars, Folders and Offline), you will not need these.
  Congratulations – your email is now in a format all reasonable email clients should use – mbox. From here you aren’t just limited to Mail.app, other clients support mbox including (ironically) Microsofts own version of Outlook for the Mac, Entourage and the opensource Thunderbird.

Getting your mail into Mail.app

• From here you’ll want to get your newly created mbx files from windows to your OS-X install. I would recommend taking only the mbox files of previous email folders you want – Inbox.mbx and Sent.mbx being the obvious choices.
• Now with them on your Mac, open Mail.app. If this is your first time opening Mail.app, setup your email accounts as you need. Once you’re all done there open Import Mailboxes from the File menu.
• Choose mbox files and navigate to the folder with your converted mbox emails in them. You can select miltiple mbox files which will be imported as separate folders into Mail.app.
• A progress bar later and you should find an IMPORTED folder, and you can now move them as you need to.

Exporting your contacts from Outlook to Address Book
Originally from macosxhints.
As you may have figured out by now, Microsoft makes it as difficult as possible to escape their Office/Exchange ecosystem, either by not including export options or making it as much a convoluted process as they can. For this we will make the files we need by faking an email with all your contacts as attachments – smart.
You can export individual contacts to a vcf file by selecting the contact and choosing Save As under the file menu. This is great for a couple of contacts but not those of us with 1000 odd contacts –

• Switch to contacts view in Outlook, Select All contacts (or just the contacts you want to take with you) and the under the Actions menu, Send Full Contacts and then In Internet Format (*.vcf).
  
• Outlook should then make a new email with attachments of all you contacts as usable VCF files. You could email that to yourself but if you have quite a few contacts, it’s best to copy the files out the unsent email and into a folder to move manually. Click on one of the vcf file icons in the attachment panes and select all. Drag its icon to an folder in an explorer window.
• From here you need to get the folder of vcf files to you mac, open Address Book and drag all the vcf’s on to the Address Book window.

Getting your calendar
This is actually the easiest part of the process.

• Switch to calendar view in Outlook and select the calendar you want to export.
• Under the File menu, choose Save As. ical format should be the default.
• Choose more options and set the date range as Whole Calendar, detail on Full, leave the advanced options unticked.
• Save.
• Again, get the resulting files on to your mac, and then open iCal.
• Choose File, Import and choose Import and iCal file
• You’ll be asked if you want to merge with a previous calendar or make a new one.
• Rinse & repeat if you have more calendars.

Things that don’t export/import.
Tasks! although these can be imported as an email folder via the Outlook Express method although tasks will be turned into emails as far as Mail.app is concerned.