Out of curosity, you say the computer has 1GB ram. Is it one DIMM, 2, or more? If its more then one, it is possible that on of your RAM DIMMS has gone bad, mucking up the system. I personally like
Memtest86 though it can be a bit hard to navigate.
One thing that I would do is disable all extraneous services. When we were setting up the webcast for monty madness, our host/encoding computer would crash out after about half an hour of encoding a broadcast because the cpu load would reach 100% for an extended period. I followed blackviper's services guide for windows, and that solved the problem. His site is down, but
MajorGeeks has a nice mirror running.
If things still don't improve, try uninstalling Norton.