Jimellow, TigerDirect has a 3GHz Celeron D (345) with Intel motherboard and 512MB for ~$118. It uses integrated graphics too, but for $118 total who's going to complain. It would compare nicely to that new Dell, especially if you can bring along some of your old RAM.
http://www.tigerdirect.com/applicati...=MCM-GVHZL-345
You'd have to ask someone else here if your Dell motherboard mounts would accept industry standard motherboards. Some Dells do, some don't. If not you could pick up another case at the same time and pull your old Dell HD, floppy, CD, etc. I just hate to see people buy everything over again when the problem isn't understood.
BTW, if you haven't already, download the latest video driver. Boot in safe mode, go to device manager and uninstall the current driver. Reboot, then install the new one. It does sound like failed hardware (vs. interference) but I'd give it a final attempt before giving up. It'd also be sad to toss things just because you have a gamma/driver mismatch. (which can happen when changing between driver versions without uninstalling completely)
Good luck however things fall.