I have a Canon A85 and it can only take upto 15 seconds but you can adjust the ISO from 50 to 400.
There are people who have done a bit of astrophotography with this camera
check:
http://www.cloudynights.com/ubbthrea.../o/all/fpart/1
But as Iceman suggests maybe you want to think scope first then camera.
These cameras cost as much as a 6 inch Dob!