[TippeX]

outsourcing, so you're going to make an image, and send that for duplication?
if you're doing that, and its not an industrial duplicator, then you cant use disk signature algorythms, and all you can do is use some encryption or stuff on the files themselves

dongle could be a good idea, but dont forget dongles can be emulated or cracked (yes, even the commercial ones)

you also need to think about the distribution media too,
do you intend for the files to be run from the cd/dvd or to be installed to hdd?

if its the second option, you could encrypt the files on the cd/dvd, and only decrypt them when someone phones you for an unlock code etc, that way you can (not 100% tho) keep tabs on who has the program...

so you've got the drm method, dongle method (probably costly, and not really worth the effort) or disk signature method (in which case you need commercial protection like securom, safedisc, starforce and so on... all of which you will have to pay for)

without really explaining the model you're using and your target audience, and the amount of purchases you expect, its hard to build up a good solution for you...