Computer Speed Question ????

I have a Dell Dimension 4550 with 1 gig of memory that is a pentium 4 with XP pro service pack 1 and it has a 2.40 ghz processor and 400 mhz front side bus. I also just recived a Dell Precision work ststion 690 ( server) I am using this unit as a single computer unit. It has a fresh load and is a Pentium 4 with a x86 Family 15 Model 6 stepping4genuineintel 3191 processor. It has 2048 mb of memory. It is running XP service pack3 at this time.  It has a 250 gig sata hard drive and I am only using about 10% of it at this time. My problem is the little 4550 wich has a 80 gig hard drive works a lot faster than the bigger 690 when doing anything at all. I was just wondering if anyone would no why this would be. I am kind of confused on this subject. Thanks for any input anyone can give me.  Herb