I am using Office 2007 and my outlook PST file is just over 4GB and I can't read it anymore.
What can I use to recover the file?
Has Micorosoft fixed this limitation in Office 2010?
Your problem is almost certainly NOT a limitation of Outlook; most of these other posters aren't really offering you a good solution.
I agree with the poster who suggested the most likely problem is that your hard drive is formatted FAT32 - which is limited to 4GB file sizes. To find out go to Windows Explorer, right-click the root of your C: drive (or whatever driove the PST file is on) and choose Properties. The dialog box will tell you if it's FAT32 or NTFS. If it's FAT32 you'll need to convert it to NTFS, which is pretty easy to do.
If that's not it then you probably need to scan your PST file for errors. See if this helps: http://www.officeforlawyers.com/outlook/tsol.htm#SCANPST