Choppy/Grainy HD Streaming Video?

It plays fine on my rig.

That's it?

No most people reading your post probably think you're a tool who doesn't know hardware or HD from a hole in the ground (oooh the awesome quality of compressed net video makes me want to get rid of my HD/BR player and HD Sat&Cable ).
Probably also explains why you can't figure out that it may play just fine on someone else's updated rig (like roadrunner), and the problem exists on your end with your admittedly outdated rig, but you're being too much of a knob to fix your defects.

Simple answer, just like those who should stick to consoles instead of gaming rigs, you should go out and buy a cable/satelite box and stop using the internet (both for watching TV and bothering others).

Pentium 4 3.0GHZ
1gb RAM
128mb VRAM

I may forget something else, but you can ask what I am missing.