It's really hard to pinpoint one single board or hardware generation that stopped xp x64 support as generally support for the platform was never very good to begin with.
I will say this, get faster ram. Judging by your system specs, It's the biggest bottleneck of your system. At least ddr2 800 ddr2 1000 at best. The cpu and board you are running can accept up to 1333 which is quite rare in ddr2 form.