This guy sells an adapter to use an SLR lens with a webcam for astrophotography.
http://webcaddy.com.au/astro/slr_to_webcam_adapter.htm
Not sure (read this as 'not experienced enough to judge') if the webcam AVI's would be better than multiple multi-minute exposures with tracking, or better than multiple short (< 5 sec) exposures untracked.
cheers,
DJDD