I've been using CS3 on an XPPro machine since CS3 came out. I've had and solved many problems, but this one has not changed since the first day: After converting a file from RAW to Tiff or PSD and working on it in CS3, when I return to Bridge there is only a generic icon for the file. No matter how long I wait, and whether the file is selected or not, no thumbnail or preview gets generated unless I purge the folder of its cache.
I use distributed sidecar files, and have done all of the usual tricks to cure this problem: I have purged cache files, purged what was left of my original central cache, trashed and regenerated preference files in Bridge and CS3, repair-reinstalled CS3 and Bridge, done uninstall/reinstall of CS3 and Bridge, and even changed my video drivers. I have tried hardware vs software acceleration. Many problems along the way have been resolved, but nothing has helped with this one.