Sony vegas avi problem

hey everyone so i wanted to ask you why i cant add avi format video files to vegas when i click import and select any avi file it shows me a eror and close the vegas
so what's the problem ?
cus every time i have to convert avi files and it takes time :/

I think everyone had this problem when we were noobs xD
Install the xvid codec ( [You must be registered and logged in to see this link.] ).

i alredy instaled it :D but when i import its just sound no video :/

There's something wrong with the audio format/codec. Go to videohelp.com , the forum and ask help.