I would be very careful about upgrading this machine as the last official drivers on HP website are only compatible with Vista.
Athlon 64 X2 Dual-Core 5000+ Processor (2.6-GHz, 2x512K L2 cache, 2000-MHz FSB)
but I'm not sure of which 5000+.
Athlon 64 X2 Dual-Core 5000+ Processor (2.6-GHz, 2x512K L2 cache, 2000-MHz FSB)