Precision 690 Slow

I have a Precision 690 that's just over 2 years old.  Last year, if not earlier, i noticed it getting very slow.  I did my bi-annual "wipe" everything and reinstalled all drivers/OS, etc. from the ground up.  It seemed nice and peppy for just about a few weeks but that was short lived.  My patience has run out and 6 months later, i'm back again with a painfully slow system.  Most of the time, it appears to be something with the disks, as it will spend a ton of time continuously hitting the hard drive(s)  Sometimes, for no appearant reason.  Other times in the middle of doing things.  Also, most of the time when shutting down/rebooting, it takes about 60-90 seconds to even start the windows shut down process, after pinging the hard drive that whole time. I literally hit shut down . . then go pack my bags . .then come back to the "confirm" popup.  I've tried other things like completely removing McAfee as i though it may be culprit, nothing.

This is my current setup:

• Precision 690, Dell Bios A08 (just upgraded a few weeks ago)
• Intel Xeon 5110 CPU @ 1.60Ghz
• Windows XP Professional SP3
• 4 Gb DDR 2 ECC SDRAM @ 667 MHz, 4x1GB sticks
• NVIDIA GeForce 9500 GT video (I just upgraded this last month, thinking it would help - nope)
• Dell SAS 5/iR Integrated Controller
• Controller: Intel 631xESB/632xESB SATA AHCI Controller
• Disk 0: Seagate Barracuda 7200.10 ST3160815AS 160GB 7200 RPM 8MB Cache SATA 3.0Gb/s 3.5" Hard Drive - OEM
• Disk 1: Seagate Barracuda 7200.10 ST3500630AS 500GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive - OEM (Perpendicular Recording)
• Disk 2: Maxtor DiamondMax 10 6L300S0 300GB 7200 RPM 16MB Cache SATA 1.5Gb/s 3.5" Hard Drive - OEM

Disk 0 was the original install.  Disk 1 and 2 were add-on's.  I've got operating system and all programs on Disk0.  Disk 1 is Data that I access alot, including a shared partition for "company data" on a simple Workgroup and Disk 2 is mostly "resources" that i don't access much, if at all during a day.

EDIT: I should note that these symptoms even appear without my small network being active.  While i thought it maybe merely the fact that i have some folders shared and accessible, it still happens when my other machines are completely shut off, NOT accessing data (not even capable of)

I've read some old (1.5-2 years) posts talking about the SATA controllers and the like, but i'm not sure if they relate.  I'm not sure i have things setup properly, or if there's even room for different setup or improvement.

I do know that I'm about at the end of my rope with this system  (similar to other posters on similar topic)  I have 4+ year old Dimension machines running XP Home and Office 2000 that seem quicker. 

Thanks in advance,

Blake