I'm sure there are more keywords to cover a good search, e.g. 'serial number' 'user registration' etc.
A very good method (my opinion) is the one discussed here,
Are you a developer who uses NSIS to distribute your application? Are you a Winamp plug-in developer who wants to use NSIS to distribute your plug-in? Have suggestions for other people like you? This is the place.
If I remember correctly, user deanbayley who applied that method, said he has no problem to give a hand if you contact him.