Quick graphics card question please

Hello everyone, I had a very simple but very important question.

Will this computer:
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c03...

Be fully compatible with this gfx card:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

And this power supply?:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I'm very confused because different people are telling me different things. Like that my mother board isn't compatible, and that a PCI Express 2.1 x16 graphics card isn't compatible with a PCI Express x16 card slot (what does the extra "2.1" on the graphics card even mean?) and that the card might not fit my case and stuff.

By the way, the power supply I want to buy and the stock 300w one are the same exact size (5.9 x 5.5 x 3.4) so I'm assuming it'll be okay, but I just want to be sure.

Its mainly the graphics card and its compatibility.

Okay thanks for your help and advice  

OH and on a side note. would a hyper 212 cooler:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
be a good idea (for longevity and performance reasons) for my cpu even though I don't plan on over clocking that much, if at all?

Thanks again