i may be a bit late to this thread. But I would like to share my experience with this issue.
Intel Core 2 Quad @ 2.66 GHz
4 GB RAM
64 Bit - Win 7
I never used to have any issues with the game on vista 64 bit. But with Windows 7, I had. I tried a lot of things from different people. However, When I changed my Bit Defender 2010's "Game Mode" ON. the problem resolved. It's just bizarre because I did have BitDefender installed even when I had vista. Something to do with Windows 7, Bit Defender & NFS Undercover Combo.
So, there you go. Try disabling any Anti-virus you may have on your system.
P.S. Please do not delete your Anti-Virus. Your system could get affected with virus within 4 min. according to the latest internet stats.