64bit processors are not needed as such by even gamers, but by the people who MAKE them.
I have trial tested lots of new Intel and AMD processors, while they are very fast, they are overkill.
But it is up to you.
I can run on a 2600+, 1Gb 400RDDR, 80Gb, 256Mb DDR GeForce FX 5600 Graphics, dual cooling all the latest games, with no problems.
It can open Microsoft word in a blink of an eye, a webiste is on in a flash. I have also run games at very fast refesh rates and good resolutions and it is impressive what comparatively low-spec processors can do, when combined with the correct gear for you needs.
after everyones good points for upgrading to athlon64 or not, be careful as there are three new AMD chips. the OPTERON, athlon64 and athlon64 FX (which is ment to be optimized for games)check out AMD's web site.
the OPTERON and athlon64 FX use the same sort of motherboard socket 970 but the athlon64 use's a motherboard that is socket 754 and the chips quite expensive, £330+ for the 64 and £640+ for 64FX.
heres a link to DABS click here as they are the only one's i have found with prices for the new chips.