fuck those other processors, get a intel core 2 duo and at least 2gb of ram, anything less is wasting your money if you plan on running vista on it
dont worry about a huge hard drive, you can always buy an external hard drive for cheap and backup your computer and documents to that and also save shit on it
here, go here (it is dell small business account) :
http://configure.us.dell.com/dellstore/config.aspx?c=us&cs=04&kc=6W300&l=en&oc=bqcwkta&s=bsd
configure that to either windows xp or vista home premium (whichever you prefer) change the display to have true life (free) and setup an account saying you have a one person non profit company (basically that you are a computer tech that works on computer for family for free on the side if they even ask) and you will get that computer for less that $700 and it will blow any of those amd processors away....if you want to beef it up, go ahead, you will still be saving money