What happens when i do that, do i get a avi demo?

cl_avidemo "30" gave me 2fps..should i use like 125? or maybe 150? Thanks for your help

Don't mind the fps you get while running cl_avidemo, it doesn't affect the actual output. It's pretty normal, considering that 30 screenshots are captured per second, each (depending on your resolution) about 1 - 4+mb ;>
After creating a compressed .avi you'll see the 30fps.

Dunno how long that will take But i wouldn't capture the full demo, unless you have tons of space.. I'd suggest to just bind cl_avidemo "30" and cl_avidemo "0" in your config and only capture the scenes you really want.
I'm not sure if this is fully correct, but here's a simple method to calculate the size of one image in your resolution..

[code:1]Resolution: 1024x768 = 786432 pixels
x 24 bit = 18874368 (truecolor)
/8 (bit to byte) = 2359296
/1024 (bytes to kilobytes) = 2304
/1024 (kilobytes to megabytes) = 2,25[/code:1]

About 2,25mb for one frame. For 10mins you'd have to multiply that by 30fps and 600secs.. So let's say about 40gb

so if i already have the demo, in quake format, i cant convert to avi? cause all i see is how to make an avi demo