The AMDs/Athlons run quite hot. Make sure that you have decent cooling in the case (especially if you have a 7200rpm hard-drive). Most mobos have 12v power-pins somewhere for an extra cooling fan and most cases now have a mounting at the front (or wherever) that is designed for an extra standard sized fan. The extra fan and bolts only cost a few quid. Fractionally noisier but worth it. I've fitted all my PCs with extra cooling.
Vacuum/blow through (Dust-Off canister) everything every couple of months to get rid of the dust bunnies. Switch off the PC and let everything cool down before you do this and let it get back to room temp after - the gas gets very cold.
Cheers Mac