Power supplies are standard, the only thing you need to worry about is wattage and quality. 350 to 400 watts should do fine. Most mid tower(16.5 in.tall) and above cases will take an ATX motherboard. ATX is the size also known as the form factor of the motherboard. There are other sizes like mini ITX and micro ATX but plain old ATX is pretty standard and I believe fits a wider range of cases. I like AMD over Intel again for the "bang for the buck" factor. AMD CPU's and motherboards are less expensive than Intel and offer similarly performance. 64 bit AMD's are not included in this statement because the out preform Intel and are still spendy in my eyes.
As for the new hard drive if you want to make it easy just put it in as a slave drive and the 20GB as the master.
It's like putting in a CD or DVD drive except you have to format(easy)it before you can put data on it.
I know it sounds like a lot but it's not as bad as it sounds. I taught myself how to build computers before I went to school and learned how.
Send me a PM if you want to know anything more specific.
99 Contour Sport SE MTX
KKM filter, B&M shifter
No res, BAT kit
Green car silver hood (because silver is faster)
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