if new...y r u still using agp...
out of those 2, i would have to say go with the fx5900
i would suggest a nvidia 6600 vanilla instead. those are around $100 and offer newer technology and decent performance.
I am building a moderate gaming PC, I have reached my two choices for my graphics card, however, there isn't much info avaible of reither of them, so I'll have to ask: Which graphics card should I choose.