i have downloaded a movie into avi format, how can i burn that onto a disc?

hi, i have downloaded a movie from isohunt.com which saved as an avi
file. i have already downloaded a program which can convert the avi
file to a dvd file but the movie is taking up 7.85 gb which means i
will then have to save the movie onto 2 discs... i was wondering if
there is anyway to make the file smaller so it can fit onto a normal
4.7gb disc...

thanks in advance