Weeelll... depends on the settings...
If you're going for a full screen (320x240) movie, then it'll be something like an hour and a half at good quality. Which is, to my mind, not enough - so I encode at ~320x196, which makes things a lot smaller. Using mono sound also helps, though I try to keep it at 22KHz, else it sounds *shite*. If you encode well, with sound like that and video at that resolution, you should easily get a couple of hours or a bit more on.
If you're willing to go even more wide-screen (i.e. 2.85:1 as opposed to the other one in DVD terms), then you'll easily fit more on. I've a copy of Harry Potter 2 that' 90 mb in total because the source was very very widescreen and I didn't crop it and such.
However, if even that isn't enough for you, then there is another option - namely, go smaller than 320
- the video will get repositioned in the centre of the screen, and the smaller the resolution, the smaller the filesize - and requisite bitrate, of course. I recently encoded Ice Age, with truly abysmal sound (but audible) and 160x120 resolution at a bitrate of 60kbs - the result was that in high action sequences, the last couple of lines weren't redrawn, but other than that, it looked pretty much fine. The filesize - for the entire movie - was just under 40mb. Ok, it was no longer good quality. But if you're after quantity, then smaller resolutions are *the* way to go.
Please note that decreasing the framerate doesn't actually have a huge effect - maybe 5-10mb at 320x240 for Finding Nemo being reduced from 20fps to 10 - presumably because of the way they're DivX works. It may have a greater effect at super-low bitrates (e.g. my 60 for Ice Age, which should probably have been 70 in order to get it to be able to redraw the entire screen; the space gained from lowering the framerate further *might* have meant that 60 was enough. But it wouldn't have looked anything like as nice...)