Course it will; that compatability is not the problem. But you will not get the power of the 9800 XT from a P4 1.6Gig - it will not handle the graphics you would expect from the 9800 and hence it would knock all of the Qualities you could play at out of the Window.
Its not really worth it; you wouldn't notice the difference between 9800 on there, and a 9600, maybe even between it and a 9400.
A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.