Got them at a local computer fair £255. I've still got other hardware from the old setup which I will replace in time mainly as y XP home is OEM & I think I have to not replace to many changes at once for the activation process... see other link going.
Currently there are no 64bit operating systems other than a Linux based one.
MS will launch one in the near future. When it does you will be in a postion to make use of it. The biggest difference will be the way memory is addresses and this will it is said bring a noticable increase in system performance.
I took the decision to go 64 bit as my machine was long in the tooth and I was going to upgrade anyway - it seemed silly to go for a 32 bit system when the reality is that 64 bit is the future.