I wanna know what is the reccomended video card to run all current MAME games?
Largely irrelevant other than as an interface device with your monitor of choice. Radeons seem to be a popular choice because they have good out of the box compatibility with PC monitors, and TV's. If it is an arcade monitor then def go with an ArcadeVGA for minimal hassle and set up.
Mame is far more dependent on CPU speed and RAM.
As far as running everything is concerned its not going to happen at the moment. Try using the search options to find out about known issues and imperfect emulation of lots of titles along with extensive FAQ's and threads regarding hardware. The information is all there.
The PC you have should be fine for 90% of emulated titles.