[MacDV] Do I need a new video card?

[Thaddeus Camp]

I apologize for the basic nature of this question - but here it goes:  
what exactly does a video card do and what benefits could I expect  
(if any) in primarily FCP (secondarily iPhoto, and Photoshop) by  
getting a better video card?

I am primarily trying to get better performance out of FCP and trying  
to decide where to put my money - RAM or improved video card. In  
anticipation of the answer "both," which would you prioritize given  
that funds are limited?

My set up is Dual 1.8 G5, relatively low amount of RAM at 512meg, 2  
external fw drive, and the stock GeForce FX 5200 driving a 17" Apple  
Studio Display and a 17" Samtron CRT.

I imagine myself to have a somewhat decent system but FCP still  
stutters when editing at "Safe RT" and medium playback quality; I  
would like to improve FCP performance and just learn what I can  
expect from getting a better video card.

Thanks,

Thad