You should have got the CD, or serial number from the previous owner, at a bare minimum.
If not, contact Hyperion and explain your situation. Not much to do other than that. You should have received a CD with it, which would have had the serial number, but didn't. Contact them and explain the situation, give the previous owners name, etc.
4.1 update 1 is a full install, not a mere patch. You burn it to a CD, it's an install disk. (That is assuming you have access to Hyperion's support mechanisms to get it). 4.1 u2 is a "patch". As much as I'd like to "help a brother out", I can't risk losing my own OS4 license rights by passing it on. Hyperion are good folks to deal with, contact them and explain the situation.
Forgive me if I'm missing something in the translation here. Talk to Hyperion for support.