Need help upgrading

[qwertyadsl]

hello guys i am trying to upgrade my graphic card to a better one and i was wondering if the community can help me out
so here is my current spec
cpu: intel core 2 dou e6300 at 1.86ghz
ram ddr2 4 gigs
os windows 7 32 bit (its a cracked one )
graphic card: Current nvidia 8400gs (thinking of upgrading to 6650 or the 7750 card from amd)
motherboard is a dp965lt
power supply im not sure how many volts it can support
once again any help will be really thankful

So im lean towards buying this one
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102985
So this one says its a pcie 16x 3.0 or something i believe my pcie is 16x version 1.0 or 1.1 will this be a problem??
If so can you guys find me the right 7750 card thnx

 

[qwertyadsl]

Also im using is 1440x900 resolution

 

[qwertyadsl]

Also looking at thus card
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150611
Which one is better one has more core clock and other has more effective momery clock