So i just dled VirtualDub to reduce the size of my fraps vids but it does not work? i just want to reduze the size of an .avi vid but it tells me always: error -2 or sth like that :/
pls help me.

http://www.virtualdub.org/docs_crashes.html
http://www.virtualdub.org/virtualdub_kb
Check those if you already haven't, also would be nice to get the exact error message.

When you load the file you must also choose a compression(in order for it to be smaller).

And you save it from File->Save as AVI or Old format avi if the first one doesn`t work well.

how do you mean that?
i usually just load the file -> compression -> divX decoder -> wait till its done -> save as avi. and than i get the error:
"Unable to initialize the output video codec"

download SUPER.
http://www.erightsoft.com/SUPER.html

very few people know about it, but its one of the best when it comes to audio/video converter.

ain't virtual dub used for combining pics to make one gif?

Not only for that...I also use it to compress some movies.