dvdrip avi files

I just wanted to know what kind of program people are using to convert their avi files?

I've tried a few programs already and none seem to work. Especially with the dvdrip divx, xvid movie avi files that I download from limewire. I get errors like can't recognize codec.

Other programs manage to convert the avi files to mpeg, but i only end up with the mpeg file sperate from the audio files. And theres no option to place the two files together.

What's a good program to use to convert avi files?

[RaaF]

I use Ace DVD backup with Xvid codec

and where can i get this program?