Can't import avi files

I got WMP 9, but while i wanna import avi.files, it showed sth about that i don't have avi codec, if I tried d/ling and installing that codec, I should close and open movie maker again, and try import the files. I followed what it showed, but it doesn't work.
But i am sure I got the avi codec as i can play avi files in WMP 9 T_T||

Please help~!!!!!T_T