I was previously using an AMD X2 3800+ on XP64-bit and decided to upgrade to Vista 64-bit. I popped in a new AMD X2 5600+ and did the install, now registering as 2.01ghz... Anyone know what is going on? Thanks all!!
Check your BIOS and see if there are settings for CPU speed. If not definitely flash the new version of your BIOS. If the BIOS registers it at the correct speed it might be possible that Vista is showing the processor at a speed step setting. (Do the new CPU's even offer speed stepping?)