I have been running the current version of PAF (5.2.18) on my current computer for over 2 years with no problems. The operating system on this computer is Windows Vista Home Basic, a 32-bit operating system.
Will PAF run on your Vista computer? i.e. Can you create a new PAF data file and add information to it? If so, there may be a problem with the data file you are trying to open, and not with the program. Or maybe you are trying to "Open" a PAF backup file. (Backups need to be "Restored" rather than "Opened".)
Try to open your PAF files from PAF's File menu. If that doesn't work, try File menu > Restore.
Let us know if you were successful. In a pinch you can email the file to me privately, and I will try to identify the problem, fix it and send it back. My private email address: email@example.com