Well I'm not sure on how you are actually ripping the DVD data, but I used http://www.dvddecrypter.org.uk/ to extract the disc info as .vob files and then AutoGK would pick it up and turn it into the .avis under your set parameters. It was a good few years ago I used to do this and I think there are more up to date programs.
Look for Slysoft AnyDVD and CloneDVDMobile. Both free downloads from their site and give you 21 days full, free usage.
AnyDVD reads the DVD data when you insert it in the drive and then removes copy protection etc. Once its done that (10 - 15 secs later!), run CloneDVDMobile, choose your settings and then press go and it will rip the movie. I use the DIVX setting for ripping and do a 2 pass run which takes about an hour per DVD.
I've just started doing the same and ripping all mine to an external HDD as I'm tired of having to drag DVDs out every time. Now that I have Windows 7 and the Media Centre works well on it, time to start building a home theatre run form the PC!!!