Ok, where to start...
Puer Aeternus had a point. It sucks. Well, sort of, it's not quite as bad as you might think....just.
The GeforceFX 5200 is based upon the 5600 core, with some vertex shaders and the likes removed a little. It's based on a 2x2 architecture, meaning it has 2 pipelines, both capable of multi-texturing. The Ti4200 by comparison, has 4x1, which has 4 pipelines, capable of single-texturing only.
What's the difference? Per clock, the Ti4200 can produce twice the number of texels the FX5200 can if they are only single-textured. If they're multi-textured, they work at the same speed. 3DMark2001 is mostly single-texturing based, and so you will find that clock for clock, the Ti4200 is twice as fast (hence why you scored 5000 3DMarks, while a Ti4200 will typically get 10000). In 3DMark03, which is motly multi-texturing, they will score more similarly (and I believe you will find that is true if you look).
So, as long as you only play multi-textured games (Doom III is the only one I know of, but that's not out yet), your performance won't suck. The only problem is, all multi-texturing games are so new, that the card isn't powerful enough anyway. A Ti4200 by comparison, still couldn't play multi-texturing games, but at least on current games it's ok...
But yeah, RMA it