Shroomism said:

Working in the GPU industry, I get calls and emails from people every single day, who think they can just slap a $500 graphics card into an old, $200 HP computer (just like this), and have some kind of super gaming system... but inevitably have tons of problems.

First of all those motherboards are very basic and not designed for handling high end modern GPUs.
(As mentioned the PSUs in almost all prebuilts are always entirely insufficient for any aftermarket GPU, you will have to upgrade that first of all)
Assuming a high end modern video card even works in the motherboard (80% of the time with an older prebuilt basic board, they do not work and there will be compatibility issues with older motherboards). Assuming you CAN even get it to work, the CPU will almost always be a major bottleneck.

In other words, if you want to build a real gaming system, it would be a travesty to just plop a high end graphics card in that thing.
You are MUCH better off in the long run starting from scratch, with a relatively modern motherboard/CPU, a 500+ watt gold PSU, a cheap-ish but decent card like as mentioned the 650Ti Boost.

With your current CPU... Benchmarks put it right under a Intel Q9300.. so I'd ballpark it around anything higher performance than a 550Ti or so, and you'll start to see some pretty heavy bottlenecking, depending on the game of course.
Skyrim is a very intensive game both CPU and GPU intensive. That CPU can probably lightly handle it but I wouldn't slap any 600 series card in that thing.
If you want to do it right then upgrade the Mobo+CPU first

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