"Windows Vienna" was the original codename for the operating system eventually released as

: The product key helps Microsoft verify that the software is genuine and has been purchased from an authorized retailer. This helps in reducing piracy and ensures that users receive proper support.

No, not a retail Windows 7 key (e.g., from a DVD box). Windows 7 retail keys are for RTM (Release to Manufacturing) build 7600 and later. Vienna is pre-RTM, pre-Beta, pre-everything. The key formats are incompatible at the cryptographic level.

Let’s address the elephant in the room. If you type "windows vienna product key" into a search engine (aside from this article), you will find hundreds of shady websites offering: