The reason I picked the OCZ is because due to the fact that it is a modular supply. I want to cable manage the case when I start putting it together, so that was one of the reasons why I wanted to use a modular supply.
Good choice I own one myself, the Corsair is a better unit for $10 but the OCZ will do you fine.
I don't know, I wish I could purchase from Newegg but I'm in the UK.
From what I understand sometimes they are missing cables, backplate, driver discs etc.
For that price it wouldn't bother me, you can get all the drivers from the website and you probably have cables.
It is a micro ATX, but you could stick a PII in it if you wanted.
Heres an ATX one - http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Anyway I'll leave that decision up to you, happy building.
However, I do have yet another question. Just to clarify, the CPU is an Athlon 64 X2 4600+ @ 2.4GHz will that be a good for the 4870? I wanted to go the Nvidia route for the GPU, but I don't want to bottleneck the CPU.