Some people with Dual core machines may notice models spinning too quickly or jitters.
Here's a link to a driver update that may solve the problem, from the other thread.
For those of you with AMD dual core machines, AMD has a driver update that may address this problem: AMD Athlon™ 64 X2 Dual Core Processor Driver for Windows XP and Windows Server 2003 Version (exe) 188.8.131.52
And here are other links taken from the same thread that may be relevant:
http://forums.seriouszone.com/showpost.php?p=688033&postcount=139Update: AMD no longer offers a dual core driver, but the optimizer should do the job.