I would buy a system with a quad-core or better CPU that also has a PCIe 16 expansion slot available and a 350watt or greater power supply. Then pick up a video card for around $100 with at least 1GB dedicated Ram. If system comes from manufacturer with 4GB Ram, I would bring it up to 8GB. All of this can be done for less than $1000, probably in the neighborhood of $600 USD if you get say a Athlon II x4 Quadcore CPU Compaq tower for $459. 4GB DDR3 Ram upgrade for less than $50 and $100 video card. If you prefer Intel you can go with Core i5 or Core i7 CPU. I prefer AMD for best price/performance buy. The last Compaq tower I bought had a 350watt power supply. If your going to go with an insanely powerful video card you might need better than a 350watt, especially if it is not powerd off of the PCIe bus finger taps. If it requires the 12Volt power connections to power supply to video card, I'd upgrade power supply to at least 650watts ( around $50 ).
I am running Skyrim on a Athlon II x4 620 ( 2.6Ghz Quadcore ) with 3GB (DDR2) Ram on Windows 7 32-bit with ATI Radeon 5450HD with 1GB Ram without issues on normal video settings. Also mine craft no troubles with, and World of Warcraft I have graphics set high and am getting 30-60fps depending on whats going on. My video card I got for $30, but I would suggest a more powerful one closer to the $100 mark so that it can keep up with modern games. Mine at $30 could start to freeze frame with whatever game comes out next that demands more GPU power. I have already gotten my $30 out of it, so it was a good card to buy time and get something better later vs sinking money into a powerful card now and wishing a year from now that I got the next best video card for the same price!
