Reformating/installing Windows 7 ENTERPRISE (Full, Not trial!)

Hi, I am trying to completely wipe my system and reinstall windows, only I don't have the CD. I've looked it up, and it seems relatively straight forward, I just need to save the iso file for the version of windows I'm using to a flash drive and run that to reinstall. The problem is I am running (and only have a key for) Windows 7 enterprise (Version 6.1 Build 7600) 32 bit, and the only downloadable iso file I can find for the enterprise version is the 90 day trial. I don't want the trial though, I want the entire version. Does anyone know where I can find an iso file for enterprise that's the full version, not trial? Or am I supposed to download the trial and put my key in somehow making it a full version? Please help!
edit: I should add that I want to reformat the computer (I don't have anything I want to save, want to put it back to factory standards), not just reinstall windows.

first you say you don't have a key then you say you do have a key, I'm confused...

Anyhow, if you do in fact have a valid key the eval or trial version should activate for you.
You may have to use the phone in feature the first time. That's not incredibly abnormal though.
You should be okay just using the iso download directly from MS.
If you wind up talking to a live person just tell them the truth. Don't make up stories.
If this is a laptop you may want to look at your documentation to make sure you can't just press a few buttons at the right time and have it restore itself to factory state. (as many of them can do that)