mencoder: re-scale and fit on a CD?
 

I use mencoder to backup my DVDs to one CD, and, since my machine is quite slow, I found that I have to re-scale movies to 576x448 in order that the audio and video be in sync during playback.

So far I did it as follows:
1. Grabbed the DVD to .VOB files
2. Used 3-pass encoding by mencoder (lavc) to ensure that the avi fits on a CD
3. Re-encoded the avi to rescale to 576x448

This is OK, but the resulting file that just fits on a CD after Step 2 will be reduced in size and quality by Step 3, so that there is signifant unused space on the CD.

My question is:
Is it possible to modify the standard 3-pass encoding method so that it also does a re-scaling (i.e. an additional re-scaling step could be avoided), and the resulting fill will just fit on a CD?

P.S.
I would be also happy if you could give me an advice how to modify the standard 3-pass encoding steps to encode to e.g. a 4-channel AC3 audio. Anything I tried so far resulted in a 2 channel sound, though I am sure that the original *.VOB files contained AC3 audio.