May I offer you a warm welcome to the CameraLabs forums. As you can see I've moved your post into the "Technical and scientific photography" forum as that is where all things astro-photographical
) get discussed.
The 40D is a great DSLR for astrophotography though the IR cutoff filter is a little more aggressive than some when it comes to the Hydrogen alpha emission line. They can be modified (Hutech
) but that means you have to employ an additional filter for normal photography. Another great resource is Christian Buil's site. He has a nice evaluation of the 40D which you can read here
The TeleVue site has a great summary of the ways of focussing an image on a sensor which you can read here
. Typically, you will need a camera adaptor such as those illustrated here
. If your telescope can accept a T-mount accessory then an alternative to the regular camera adaptor is a T-mount adaptor such as the ones here
. You may or may not need an extension tube to get the camera to the focal plane.
The best possible accessory once the camera is mounted is a notebook computer so that you can use remote Live View. That makes focussing so much easier and once you are set up you can use the same Canon EOS Utility software to control the camera unless you already have dedicated astro software (MaximDL springs to mind, though I haven't used it).
Have a browse through this section. I've added a few posts of my own but if you want to get really serious have a look at posts by cybermystic