Get an Athlon XP Mobile, The multiplyer is not locked, which makes it easy to overclock. I upgraded a system last year with a new Motherboard, Processor and memory. The Athlon XP 2500 Mobile was able to run at the same speed as an Athlon XP 3200, 2.2GHz (200 * 11) with a 1 degree C increase in temp. Since the multiplyer can be changed freely there are no timing issues that can can cause instabilities usually associated with overclocking. I got a Thermaltake ALX-800 heat sink for $16, the processor cost $89, DFI Infinity N Force 2 Ultra MOBO for $90, and 1 GB Corsair XMS TwinX 2-2-2-5 low latency DDR 400 memory for $160. Have fun