I guess it is a dual core problem. I don't know about Win 7, but XP requires that affinity be set to 1 CPU for t3.exe. There are threads around here that deal with that. Sorry, I don't have time right now to find them. Maybe a search for affinity will find them.
To test this theory, you can start T3 but not go into the game, then hit CTRL-ALT-DEL, go to the processes, and set affinity manually. There are two exes you need to change. T3 and t3main. One calls the other, so both are running as processes.
There may be other Win 7 issues that I am unaware of. Search here and at TTLG.
Please post back when you find the solution. Thanks.
"What we've got here is a failure to communicate", the warden (Strother Martin), Cool Hand Luke