Slow and unresponsive system under Windows XP Pro

My Dimension E520 didn't come with a floppy, and I couldn't find the right drivers anyway, so I installed Windows XP without RAID. There is only the 1 disk - the original 250GB SATA. It installed OK, and I was able to install all the drivers on Dell's website. The problem is, it runs like a three-legged dog with rabies.

 

I wiped the original Vista installation because it was slower than my old Athlon 3200, but even under XP the system is slow. It seems to be HD related - HD activity causes 1 of the cores utilization to soar and makes the system unresponsive for minutes at a time sometimes.

 

Someone please tell me what I'm doing wrong - surely a new core 2 duo system with 2 GB of DDR2 RAM should run faster than an old Athlon. If not, what did I spend all that money for?

 

Another, possibly related problem is that there is an 'Unknown Device'. The only bit of info XP will give me about it is 'AWY0001' if that means anything to anyone.