I would seriously recommend checking your RAM. I don't know much about the particular RAM you're using, but I know with my old PC I had many BSODs and random crashes and it was completely caused by one of my RAM modules.
I have a very similar setup to yours and I have literally not had one single BSOD or system crash in about a month of runtime. And I've overclocked considerably, with the stock heatsink/fan.
Try a Memtest86 overnight and see what it tells you.
(My previous system had one bad stick out of two, and upon replacing it it's completely stable. I think that the vast majority of WinXP BSODs are caused by RAM.)