I have:
AMD Athlon II X2 255
Radeon HD 2400 Pro

I tried different browsers, reduced the graphic configuration to lowest (it was almost impossible though, the game is so choppy that you can't even go through the menus). The game is slow, sounds are choppy as well, it's completely unplayable. I know this is not a state-of-the-art machine but dang, a game with quake 3 graphics should not be too much for it.