It's annoying that this doesn't work for you, I assume you've played other demos or just FPSC stuff and it's mostly OK?
Not sure what I can do about it apart from take out a bunch of stuff, but that doesn't really help with making a good game.
Oh well, it was my first attempt, I've got plenty more ideas, I'll just have to keep them simple.
Not sure about your sempron though!
I've got an AMD Athlon 64+ 3000, but the other PC I tried it on is a stock compaq with a P4, it's got a 128Mb ati 9200 that I added though, as before even FPSC was unusable.