I have a Dell Latitude D630 that has an Intel Core 2 Duo with 2.50Ghz. The user says it suddenly got much slower and a check of the processor says it's running at 772Mhz instead of 2.50. I updated the BIOS and checked the BIOS settings. Speed Step is on and claims that off would set to the lowest. I have performed anti-malware scans, no new applications, disk is defragmented, etc...
I set the power option to 'Always on' - No change
I looked in the dell area for 'Microsoft Speedstep fix for XP' and found some but none will execute on the Latitude D630 - Says not supported system. I checked the downloads and updates on the Dell support site and couldn't find anything for that particular system.
The physical machine is very clean with no obstructions to the vents and the fan seems to be working just fine.