I have the same problem. I found a workaround: ctl-alt-del to start task manager, then go to applications undercover, then go to process nfs.exe, and then to set affinity and disable all but one cpu. This solves the issue with autoscuplt, but slows down the game, so after you make the autosculpt changes, you'll need to go back to task manager and change nfs.exe affinity back to enable all cpus.
There was also an issue on older systems and some NFS games that would run slow, where the workaround was to go to affinity and disable cpu 0, back to game, then back to affinity and enable cpu 0, then back to game.
I have the EA DVD version of Undercover, with patch 1.0.1.18, which includes the challenge series and the 3 bonus cars you can win. I have a multi-boot system, and I'm running Undercover with Wndows XP Pro 32 bit.