The FindFirstChangeNotification API (used by the Wait action in all versions of Visual Build) can have problems with network shares (see
http://support.microsoft.com/kb/188321). Perhaps it was more reliable in Win XP?
You could always roll your own -- create a Loop step that waits forever, and in the loop an Exit step to exit the loop, configured to pause for a few seconds and a build rule to execute only if the file you're looking for exists ([vbld_FSO.FileExists("%FILENAME%)].