Help newbie here - error message - no decompressor

[junks]

Hi Just downloaded the software & tried it for the first time, it's going so far then I get a message

Avisynth open failure:
AVI source: couldn't locate a decompressor for fourcc xvid
(C:\Documents and settings\Administrator\Desktop\Avi\avi2dvd_temp\Avisynth_scipt_file.avs,line2

Help much appreciated as I'm not very good with PC's!!