Please help me!

I have a problem with an error when I'm trying to render to AVI (PAL) format (or just preview it!):

An error occured while creating the media file .

OS: Win 2000 (SP2) (Swedish)
DX: DirectX 8.1
CPU: 650MHz Athlon AMD CPU
RAM: 256MB
MB: ASUS K7M (Slot A)
Graphic: Matrox Millenium G400 Max DH (but DH not enabled)
Sound: Sound Blaster Live! 1024

Any suggestions?