This game has given me loads of problems.
Reinstalled XP + DirectX 9 + 9.3 Cataylst drivers + Steam + HL2:DM and whatever settings, the game is very, very choppy

Lockdown map - hit a barrel with the gravity gun and it flips slowly with loads of frames missing. The fps counter says it's doing 70. If I shoot the barrel, it explodes and the fps go into the red. It also makes the mouse very stiff and difficult to turn without getting stuck. Sure the mouse isn't the problem tho.
I have no idea what's making this happen.