I hope your *friend* realizes that is completely illegal, and advertising such practices anywhere can get you in some serious trouble.
To answer the OP's question, I'm not 100% sure about this, but I don't believe there exists (or will exist at time of writing) an actual upgrade license for Windows 8 Enterprise, as this version is only available via Software Assurance customers, and MSDN and TechNet subscriptions. You will be able to perform upgrade installs from Windows 7 Professional to Windows 8 Enterprise, but I'm speaking strictly in terms of the license, not what you can actually do with the software. Therefore, I would assume that your Windows 7 license would remain valid.
I would wait for someone else to confirm though, since as I said I am not 100% sure about this.
I also have to ask, why haven't you gone 64 bit yet? I will be overjoyed the day Microsoft finally says they won't be doing another 32 bit version of a desktop oriented operating system.