Roy.
IF youre on about the webcams for planetary imaging, then go get a toucam pro 1 or 2, it has to be the pro version, there is a third model, the name escapes me, Frank has one if you wanna ask him the model no.
You unscrew the lens from the front of the camera and buy
http://www.astromart.com/classifieds/de ... _id=582461
I know its sold but do a quick google search and you'll find one, the cameras are no longer sold new so you can get one off astromart/ebay.
You slot this into the eyepiece holder of the scope instead of the eyepiece, as simple as that, although i wouldnt call this "building a webcam" as there used to be serious mods back in the early 2000 for deep cooling and using these webcams for long exposure deepsky imaging. Go do a google search on this if thats what youre on about.