What should i look for in a video card 512mb or the number like 7800 on a geforce card?

MB that's for sure but it really has to do with memory one is ddr2 and the other is just newer and 1/2 the memory but is a Gddr3 which is I'm sure faster then ddr2 but how much faster I can't answer that one. Try one return it and try the other, see what one performs better. I would personally go with the higher MB. Not to mention the HDTV ability if that matters to you.