anyone know a program??

[Nsane]

does anyone know of a program where we can change .dem to .avi

[Multiplex]

This cannot be done through direct conversion because .dem files contain no audio or video. Those files only contain game data such as waypoints for your movement, actions, and all of the other variables necessary to reconstruct the scene which you recorded.

For a workaround try using fraps or the windows screen recorder to record your screen output while you replay the demo within counter-strike. It should be a similar result... maybe some minor loss of quality.

[Blis]

Or when playing the demo if you type in console, startmovie demoname.dem it should create an image file for each frame and a wav file for the sound.You can then use a program like Videomach to put them all together to make an avi.Try fraps first though as doing it this way can be tricky.

[TrinitronX]

Yeah... the screenshots and wav file way is how I made this machinima movie with Dr. Kleiner singing. I am unable to post a link right now, as the site that's hosting it is down. When it's up again, and if I remember to.. I'll post it.
I used Videodub to put it together.. it's pretty easy to do, and yields a high quality video. Here's a very good guide on how to do it.. with pictures and everything. It's a pdf just so you know: http://webpages.charter.net/tknott/other/hl2-movie.pdf