(Notes) Up until now I've been using a stock HP e9110t, the Radeon 4850 1 GB that it came with hasn't been doing to well with the new games like BF3, MW3 and TES: Skyrim. I was originally going to upgrade the GPU only but my PSU was lacking a second 6 PIN connector.
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I see no reason why those would not work, but you are starting to get to the point that the cpu will become a bottleneck(not saying its that bad yet.).
Those two components will be a good upgrade and the cpu is a quad core which will help even more if you could overclock it a bit , try to get it closer to 3ghz.