You mention a Pent 4 640 CPU. Was that the stock CPU for your XPS GEN 4? I only ask because I have a GEN4 also, but with a Pent 4 560 (3.6Ghz). For some reason, I thought the GEN4's could only use a 5XX series Pent 4 CPU, and the later ones needed a GEN5 motherboard.
Anyway, I've updated the ram in my GEN4 to 2MB, and added a ATI X1950XTX and left the CPU stock, cause I didn't think cost was worth the little gain. I could still play most newer games with the system as it is currently. Although I did just get a new 420 XPS with a 880GT last month, so the GEN4 is now sidelined to network storage and watching cable video on.
I'm curious too what other GEN4 users are using for their CPUs.
Sounds like you've got a solid system there. You've now made me curious as well about upgrading the CPU in a GEN4.
A couple of questions for you. Are you running Vista on your system? And how did you get 3MB of ram? I was wondering if I can replace the stock 2 512 sticks of stock Dell ram in combo the 2 1MB aftermarket sticks of ram I got from Crucial. Should all be the same speed.