Syncade

Hey. I bought the Windows 7 Home Premium (meant to get Professional but oh well) on the student discount. My computer messed up and I am RMAing parts right now.. so I dont' have it to check yet.. but if I install windows with a Windows 7 disk (full install disk).. and use my upgrade key.. will it still work? I don't understand why they want to issue upgrades or full installations. I figured a serial key is a serial key and will work with upgrade or clean install??