So you got a new DVD and want to make a backup on your computer? While you won't be able to play a DivX movie on a DVD player, any computer with the DivX codec installed can watch it.
(Note: Not DIVX the rent-a-dvd thing, but DivX ;-) the MPEG4 codec)

What you'll need installed:
DivX Codec:
http://divx.ctw.cc/index_main.html
FlasK MPEG - (try and get it optimized for your processor)
http://www.go.to/flaskmpeg
A DVD Ripper - A list of them:
http://www.digital-digest.com/dvd/downloads/ripping.html

Step 1 - 20-40 minutes
Rip all of the DVD files onto your harddrive using the DVD ripper. You don't actually need all of them, just the set that has four or so one gig .vobs in it. Usually its VTS_01_0.VOB to VTS_01_5.VOB. Be sure to copy all the files in the set (especially the .IFO).

Step 2
Run FlasK after the files have been copied, choose what langauge you want to use.

Step 3
Goto File - Open DVD and open either VIDEO_TS.IFO (if you copied entire DVD) or VTS_0#_0.IFO. Select the video and audio tracks you want. Be sure to choose the right ones- the first audio track isn't always English as most assume.

Step 4
Goto Options - Select output format - AVI Enocder
Also under Options goto Global Project options (export movie settings)

Step 5
Under the Video tab is where most of the tweaking goes on. Most DivX rips are 640 wide and whatever tall. If you do plan to keep it at 720 (or however wide the DVD is), not only will it take about 50% longer to rip, but you better have a fast (800mhz or higher) computer to watch the movies with out flickering/stuttering. Shaving off that extra couple pixels really helps.
Click the Show Output Pad to even further shave off extra stuff. I HIGHLY recommend that you crop out the extra black if the DVD is a widescreen.
The Files tab has the location of the resulting AVI that you'll be making.
Most of the other settings are fine at default, you may want to tweak them though.

Step 6
Under the Run menu select Start Conversion!
Click Select codec under Video. Choose between either Low or Fast Motion. I prefer Fast motion because you can really see the lag/jumpy frames in Low Motion video. Yet some people like their slow landscape camera pans to look really, really nice.
Now choose your Audio codec- you'll have to experiment with this. You can get by with 96kbps MP3 compression, but 128 is the lowest I use. Keep in mind that not only will higher quality mean more space, but a faster computer to watch smoothly.

Step 7 - 6-19 hours
That's it! Now sit back and wait for a couple hours/days while it compresses the video. My 800 Athlon with 256megs of RAM can do a 2-3 hour movie in about 5-7 hours (Highest Priority).

Step 8
So now you have a 700-1200meg AVI file, but want to burn it to a CD. All you need is a little program called AVI Chop. I couldn't find any homepage URLs for it, so either check DVD Digest's site or do a quick Google search. There's probably other free programs to do it the same thing, but all you have to do is specify where to chop the file and then watch it go!