help vista wmp 11 streaming NOT

I swear when I first got vista installed, I installed a codec package and I
was able to watch streaming AVI files. In old XP you had to download the
entire file before it would start playing. NOW vista has stopped doing it,
and I don't know what I have done and at this point I'm beginning to think I
am crazy.

I was able to view avi video files while downloading. I could click anywhere
on the video line and it would fast forward and backward to the point in the
timeline where I clicked - of course with a delay, but with the ability to
view while downloading and forward and backward while downloading.

NOW that is all gone. Even with WMV files, it will only play as far as it
has streamed and it will not allow any forward or backward movement on the
time line until the entire file has been downloaded. With Avi files - you
can't see anything until the entire file is downloaded.

Any thoughts.?