the graphics card should run it just fine... the FX5200 is newer than my ti4200, even if it slower...
you have to think...
a 800Mhz Duron, 256 133Mhz SDRAM, ECS K7SEM+ MB, with a ti4200... your processor/memory blows right by that... and it was a reliable machine... it could play almost anygame... we hit some lag i the new 2004 released games... but overall for a 4-6 year old computer it did pretty well...
i see no problem with your computer running halo... it wasnt that much of a performance game...