Jawa i love you man!!! but the GFX card is a tad bit low.... as might be your RAM.
The commands you've used would probably help the most, but other than that once all settings are done, it goes down to hardware. 256MB card or 512MB card will defo shoot your fps form 15-20 to 50-60. your RAM if your running XP should be ok, but id try to get 1GB and sell your 768MB should be be like €10 difference.
Your processor you should just set back to 1.33, you'll need the 2.6 as I used to have one of these and they work fine
Sorry dude but unless someone else can think of something please post, but i think your hardware boost ups will go a long way cos your internet is fine!!