[Babul]

the Athlon x2 5200+ is one of its fastest canidates. i assume its socket is AM2 (+), so an update to your hardware will also need a new mainboard, incase you tend to buy a PhenomII or even better (which uses the AM3(+) socket). this will also require you to buy new Dimms, the old DDR2's wont work well iam afraid.
maybe waiting for the new AMD 6/8core CPUs is worth waiting a bit more, why give up your 2600 MHz clocked cpu anyways?