I'll keep this post brief: You know Processor technology moves extremely fast with variants like A64, Opteron, A64FX etc. You probably are also aware of different core technologies: Newcastle, Prescott etc. Of course you are aware of difference sockets: 754, 7 etc. Want to tie all these together? Until now I used to spend hours surfing when doing a PC upgrade. Again wikipedia has come to the rescue with concise articles containing all the relevant information in one place, for those interested I suggest starting on the Athlon 64 page:

http://en.wikipedia.org/wiki/Athlon_64

Those who still build their own desktops will thank me for this tip. My current contract allows us to use our own hardware and running my (year old) A64 with 2GB and a 10,000 rpm HD is heaven - the productivity gains are enormous when I am in a real heads down coding effort. Shaving just seconds of alt-tabbing and compile times to the point where they are almost instant makes an unbelievable difference.