Poor Internet connection on your end or the host's end (or too many players; some potentially with poor, slow connections).
I agree with Kosh about the video card upgrade.Let's list the problems:
1.) Did you apply the updates to Halo? There is a known glitch with the lens flare that the patch solves.
2.) Upgrade your video card or lower the details/resolution - 3D games like higher end cards.
3.) It could be your connection, but that's doubtful. What's the ping of the server you are connecting to? Choose one with a low ping.
RAM is fine. Machine is not bad, it should be able to play Halo.
It is playable on a Quicksilver Dual 800, I had one, but you have to lower details or resolution and in some places there are slowdowns (especially with alot of characters). It also helps to have a better card.I had a Quicksilver 800 and Halo was unplayable in single player mode - the framerate was horrible. This machine can't handle it imho, especially the extra processing needed for internet play
The human eye does not notice an increase in FPS after 50 frames per second.When you are playing online frame rate is everything. 60fps = death.