The slowest core2 desktop CPU is 1.8GHz, plenty fast enough. I run Win 7 Ultimate on an Atom, no problems.
Tosh, if it's been like that since installation, I'd disconnect from the internet then disable the antivirus, to see if things improve. If they do, change the AV. Microsoft's own is lightweight and fast.
You might check the hard drive DMA mode (1 to 6, higher is better if supported), just in case, and your guru might want to check the slim chance that the controller's using PATA emulation rather than AHCI. My guess is the antivirus, though.