Well folks, wasn't I pissed when BF2 started crashing to the desktop a few hours after I started this thread. To cut a long story short I flashed my mobos BIOS to the latest version. This reset everything in the BIOS and as a result my overclocked CPU (an Athlon 2500+ at 3200+) was set to standard speed. I left it at that to see what happened and BF2 ran fine. Have been really enjoying getting my arse kicked by people I never even see, crashing helicopters within 2 secs of take off, etc. I don't know if the BIOS update solved my problem or if the reset to the standard CPU speed sorted it. I'll oc the CPU tomorrow and let you know how I get on.
BTW my mobo is an Abit NF7S v2 and I flashed it using the excellent downloadable mobo flash util on Abits website.