>How can I protect my software from being copied.

You could fill it will horrible run-time errors like Micro$oft does <g>

Between registry keys, a mess of distributed .dll file requirements and an occsional hidden system file, you could make it extremely difficult to copy the program without the install file. The freshly-installed files could ask for a registration number to activate (create your secret authentication file somewhere) It depends on how uptight you want to make it...

I wanted to know when my code entered a given situation. At the top of the routine i placed another routine to force the user to call me for the unlock code. They had to tell me the number the program gave them (int(1000*rand())
I would put that number into a key-generator program i had here, which would interate through the rand(1) field a number of times, and return the unlock key. The program had the same algorithm, and expected that particular unlock key. It worked great because it would be a nearly-unique key/lock for every occurance. My boss then had me take it out because he didn't want us to be called for keys...