Like everyone here says, release a crippled version as trial and then give them the full version when they pay. But then they might pay and then share the software thru p2p.

Copy protection wont work cos the minute u come up with new copy protection someone comes up ith a crack. also u waste too much time on writing copy prcotection code when u could be improving ur software.

My sggestion is to forget about it and concentrate on your program. And get the fulfillment from writing a great software rather than wriiting ok software and wasting ur time figuring how to copy protect your software and getting frustrated in the process cos half the time it wont work well enough.