Ehhm I know a tiny bit. I've seen a guy do that once and believe me it's very difficult. Don't expect to break new copy protections and stuff yourself. The guy used w32dasm and hiew (he was still learning himself - I asked him to crack a few things but they were protected too well.)
His approach was to search for the right string reference in an .exe like "insert cd". By double clicking he got to the part of the program where the protection was and hen removed or altered that part in hiew. He used that method to remove the cd-check in unreal (1).