As far as the 64-bit thing goes, you can completely ignore that as a reason to buy or not buy any processor at this time. The extensions do not add appreciably to the price. The difference in the price of the procs you list above is mostly bacause of the 2MB L2 cache. Full-speed cache memory is expensive. As far as the 64-bit extensions (AMD64, x86-64, EMT64- they're all the same thing. You will not use them in the near future. There is almost no software available for home use on Windows XP 64bit (which in hard to find). Now of course if you want to use Linux you have some options. Most games are not among those options. All of the 64-bit consumer processers run just fine in 32 bit mode. So essentially just ignore the 64-bit line when comparing processors for now.
