The obvious problem with system-locking a program to a computer is the exact same thing you asked about in your second post, adamm...what *if* the owner changes their hard drive...processor...etc...if you want to system lock the program it would obviously have to *allow* for minor changes and modify its internal security to match.

There's many different methods you could use, taking info like processor speed, windows cd key (IIRC it is stored somewhere), hard drive IDs, graphics card type, BIOS type, network settings etc...the more different pieces of data you collect to build the security database, the more you have to allow to fail and still let the program run.

G'luck with it :-p