My suggestion is that you avoid the dual boot stuff if you don't really plan to dual boot the system in the future. Make copy of your personal files, then just disconnect drive with illegal operating system and connect drive without operating system and install operating system on that drive. Run on one drive. If you like it, connect the other drive to system and format it and restore your files.
If you don't like it, plug in the old drive, boot from it and format the drive you recently installed Win 7 on. My bet is if you are comparing Win 7 and Win 7 Ultimate, you won't notice any difference unless you are a power user. If you gave the repair guy your media, I assume you don't have your license key. On most laptops, the license key is stuck on the bottom of the unit. If you have a desktop, I don't think that is the case. Before doing anything make sure you have the original software license key.