Virtualdub halp!

I made some avis with some shit program and they use xfcodec.
I tried to open the AVis with windows movie maker but it says it doesn't support the xfcodec or something, so i tried decompressing the AVI with virtualdub but than...

I get this message :

Couldn't locate decompressor for format 'XVID' (unknown)...

:?

halp pls