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#31
the 460 will certainly be a big improvement over what you have at the moment.
it's a case of how much do you want to spend? the more you spend, the better the card. read the reviews, and make up your mind.
all the cards will be compatible with your machine, once you've upgraded the power supply unit.
the only extra thing if you go with the 460 is you will need to uninstall the ati drivers first, replace the card, then install nvidia drivers. not a complicated process - especially as you'll be having the hardware replaced by a shop. it shouldn't take more than an hour all done if the guy knows what he's doing.
*edit* the ocz psu you link above is a very good psu indeed and will last a good few years.