DVD:Rip Unbuntu misbehaving for me

Hi

I have Ubuntu 8.10 (both 32 and 64 bit) and run dvd::rip.

I am trying figure out the bitrate setting to transcode DVD tv epdisodes to AVI
I am using the AVI container, xvid4 at a frame of 25 FPS.

If I as setting the bit rate at say 5000 kb/s and the estimated file
size is 1.4G
What has happened if the file size is only 700MB?
Did DVD:RIP ignore my settings?
Is this an average bit rate and the transcode simply did not meed such
a high rate?

Looking at the transcode command parameters, I am assuming the -w
5000:50 is the parameter that set the bit rate.

I am sure it is a lack of understanding on my part as I have just
started to do this on a Linux system.

Regards,
Gerhard