Anyone making the step to photographing birds faces quite a few dilemmas, camera choice being the big one, but the digiscope or DSLR option needs serious thought in respect of what you want out of your photography.
Although I use DSLR’s I think that for anyone making the first step, the digiscoping option is the way to go until you feel that you are sufficiently interested to make the move on to a DSLR and long lenses. The reason being that most of the compact digital cameras that will fit to a scope are capable of 5 megapixels, only 1 megapixel short of the most commonly available digital SLR’s which are about 60% more expensive before you buy a lens!
As an example, a Coolpix will cost £450-500 and an adaptor will be £100 plus cable release £30-35 at the most, your total outlay will be £600 approx if you already own a suitable scope, a 6 megapixel DSLR will be anything between about £800-1500, with a 400 or 500mm lens anywhere between £800-1300 you will spend in the region of £2000 you will also need a serious tripod, possibly as much as £300, getting into serious kit the sky is the limit, with a Canon EOS1Ds and 600mm IS setting you back around £12000. A lot of money to spend if you find that bird photography not for you, and a pretty big loss if you then resell the kit! It is also very heavy to carry around!
Digiscoping will yield much higher magnifications thus you are more likely to get pleasing results within a short time. You will also learn all the basics of exposure and which modes to use etc. Given that digital cameras are getting more advanced at a very rapid rate, the chances are that the resolution will be higher and the cameras cheaper when and if you want to upgrade.
Using a DSLR and 600mm lens combination will give you about 12x mag with a full frame sensor and 17.2x with the smaller sensors that are in the 300D, 10D and D100 and similar, so using this set-up is to some extent a lot more fieldcraft/patience dependent.
The dilemma really is whether you want to carry on birding and get images of what you see, if this is so, then digiscoping is the way, as its more portable and gives higher magnification. Whereas the DSLR option will require more work to get close to the birds and has the weight penalty.