With UAC enabled you cannot map drives in a logon script that is assigned using a Group Policy Object (GPO). The GPO logon script does run, but under a different security context, so the mappings get lost.
Microsoft provides a sample script, called
launchapp.wsf that works around this problem by running your real logon script a moment later under the correct security context.
It is available here: http://technet.microsoft.com/en-us/library/cc766208(WS.10).aspx
Look for the section titled “Group Policy Scripts can fail due to User Account Control” and also Appendix A, which is the source code for
launchapp.wsf does fix the problem of mapping drives on Vista (and Windows 7) PCs that have UAC enabled. However, it causes another problem: it doesn't work in Windows XP, so XP computers show an error instead of running the logon script.
Fortunately XP computers don't need the launchapp hack, so my company made a modified version of launchapp that tries to do things the Vista way, but if that fails (because you're running XP), it just launches the real logon script straightaway. I can’t share this with you as it’s internal to my company (has real server names etc.) but it wasn’t too hard to do.