That 200mm f2.8L lens you have is no slouch either...
http://philhart.com/gallery/Astropho...ic_rz.jpg.html
Cooled/modded camera obviously makes a huge difference - but good glass is the starting point.
Don't listen to those low iso 'jessies' (
)
IMHO, iso 1600 is the sweet spot on the 40D (best bang for buck point!) - BUT, you must compensate for the noise with loads of subs.
Phil Hart gave a great talk at the Astro Soc of SA stating that point with maths and images a few months ago - if you don't believe me, ask him!
Give it a try on a cold night - what have you got to lose?