Hi Mick.
If yo have a look at the Icemans images of the planets (
Images) you will see what can be achieved using a Dob and a webcam. You do however need either one of two things to be really successful, an eq platform for you dob, or extreme patience. Mike (Iceman) also written a review on imaging through and with a dob
here . Have a good look through both before coming to any sort of decision.
Webcams do show in real time on your laptop screen but rarely if ever as good as what you see through the eyepiece yourself. No DSLR that I know of that will show real time. You need to capture first and then download and then usuall process to bring out details.
If you are thinking of using an slr without equatorial tracking then your exposure limit before star trails start to appear is T (sec) = 700/FL (approx) so the longer your focal length the less time you have. With a 50mm camera lense you will have about 14 sec before trailing will appear in your image. With a 1400mm FL scope you have about 0.5 sec before your stars start to elongate into trails. If photography is only a passing interest then try a few afocal shots first with a digital camera shot through the eyepiece and see how it feels for you before diving into the money pit.
Cheers