If the stock defrag finishes and you still see a slow machine my bet is it's not the fragmentation slowing the machine. There are some that spend weeks of each month running defrag and we can't help those.

But if you run Windows XP do try flipping the IDE channels to PIO and back to DMA first as well as being spyware and pest free.

Read http://www.microsoft.com/whdc/device/storage/IDE-DMA.mspx on how to flip the modes.

Use EWIDO and HOUSECALL and dump what they find.

I also see you don't have SP2. Very strange.

Bob