Please be kind--I'm new here!

I'm having all kinds of trouble with my Mbox/Pro Tools setup on my PC.
After a few seconds of recording or playback, I get an H/W buffer
interrupt error. The message suggests that I increase the buffer, but
it's already at max (1024).

Here's what I've done so far:
- shut off hyperthreading in my BIOS
- tweaked my system for maximum efficiency (no visual effects, virtual
memory set at a constant size, system optimized for background
processes)
- defragged my HDs
- freed up an entire internal IDE HD for exclusive Pro Tools use
(111gb)

Sadly, I'm still having problems. Same business happened on my laptop.
Anybody else have these problems? I'm perplexed. My system's very new
(home built): 2.81GHz, 1GB RAM, XP SP-2.

Here are some culprits/possible fixes:
- I have NOT upgraded to Pro Tools LE 6.9 (I tried doing that earlier,
but it resulted in bringing up New Hardware Found messages on boot when
there shouldn't have been any, so I reverted to 6.7). Should I give it
another go?
- My system disk is a SATA + RAID. Pro Tools recommends against using
the system disk to cache, but maybe its increased speed will help?

I noticed that Digidesign released an Mbox2 recently. Anybody wanna
trade?