Yes, you can trim the .pst file in Outlook 2007. The first thing that you can do is to reduce the Exchange mailbox size by deleting or archiving items in your mailbox manually. Also you can select Tools → Mailbox Cleanup → AutoArchive to archive using Mailbox Cleanup.
The other option is to Split the large .pst file into multiple .pst file. You can use one of these steps.
-Archive feature to move items to a new .pst file
-Move to Folder feature to move items to a new .pst file.
For more information you can visit - http://support.microsoft.com/kb/932086
There are also some good third-party software which successfully