Help me choose

should i go for the http://www.amazon.com/Source-210-Inch-ELITE-Inch-Midtower/dp/B005869J4O/ref=pd_sim_sbs_pc_12

or the http://www.amazon.com/dp/B008QVQXS8/?tag=pcpapi-20

my specs will be: 

AMD Phenom II X4 955 Black Edition 
ASUS M4A79XTD EVO
Mushkin Redline 8GB (2 x 4GB) DDR3-1866
Samsung Spinpoint F3 HD103SJ, 1TB
AMD Radeon HD 7870
NZXT Hale82 80 Plus Bronze ATX 650W

and what are PSU's? do i need them?

Based on looks i would get the msi. PSU=Power Supply Unit. You only need one if you want everything to turn on and run.

Oh alright, its just for turning the computer on? and does everything fit in it?

Does it come with an PSU? if not, wich one should i get

would go with the NZXT since it has some cable management holes. 

they both don't have a PSU installed already, this one should be fine for your build http://www.amazon.com/Corsair-Builder-Watt-EPS%C2%A0-CX500/dp/B0092ML0MY/ref=sr_1_2?s=electronics&ie=UTF8&qid=1354993113&sr=1-2&keywords=corsair+psu

That was just my lame attempt at humor the psu supplies power to everything in your pc.

i already have a powersupply of 650watt. is that good?

I would go for the nzxt the psu is at the bottom and that is good and its toolless and toolless = easier and faster also it has cable magenment holes as Cru3L139 said

 and for your build 650w should be fine

sh*t ive already ordered the MSI. is it alot more difficult to mount the PSU somewhere except the bottom?