Dual booting OS'es with XP would work, would want a 1gb or more videocard IMO. Anything through GTX7xx series works on nvidia's side and a few 9xx series work.

XP 32-bit is only going to use 3.xxGB of ram. You will want 32-bit OS for more compatibility if games are what you have in mind.

Before anything get the system running stable though or all is a waste. First clean it out if you don't do that often. Try default clocks. Possible failing PSU.

For soundcard a creative X-fi would be good with onboard 64mb ram for DOOM3 and supporting games.

Yep, XP 32-bit, which is why I wanted to drop down to 4GB of ram.

I intend to rip the thing apart and give it a good cleaning, redo the thermal paste, etc, before I try and set it up again. It's been running with nothing but occasional cleaning of the dust filters in the case since I first put it together.

I noticed the GT635 card has XP drivers on the nvidia site, but not sure if they'll work with the card since it's a Dell OEM? The most recent Tom's GPU hierarchy shows the card as roughly equivalent to a 4650, so I dunno about keeping that around or not, but it 100% draws less power.

The problems could be either thermals or power related. FX CPUs have a rather low maximum temperature. it is 62C for fx 8350, I believe the 6000 series has a slightly higher max temp around the 65C mark.

FX CPUs are real power hogs, particularly overclocked. A Low quality or old and used PSU can be rather easily overwhelmed when trying to run an overclocked FX CPU.

Personally I would not overclock FX CPUs most of the time or at least not very high. The additional performance does not make up for the (massively) increased power draw and their susceptibility for overheating makes cooling them a big issue.

Well, assuming the parts aren't damaged from the 24/7 usage I've been giving it, the plan is to run it at stock once I repurpose it. I'll know for sure when I rip her apart for a long-overdue cleaning.