If you mean the common version that you buy at stores like Home Premium and so on. By LAW all Laptops on Display must show a valid Key sticker on bottom.
Many will simply look for a laptop with the exact version of 7 and flip the laptop up and copy the key. However- you don't need a 2nd key to install if you have the same version already on DVD as the one your speaking of. The sticker is underneath that laptop and you can use that one. I put XP on my Brand New Laptop.
I CAN'T stand Windows cause to be a UPgrade it MUST do more than previous versions. What it does must also be done with less resources.. XP can be ran with 64 or 128mb or RAM. Yet it requires 2GB on Windows 7 for (Windows XP Mode) according to their paperwork. JOKE! Then they made many of their apps incompatible with ALL previous Windows versions. Sorry- sore topic with me!
Hope this helped and I am sure it did at least save you $.
P.S. You can run the 32bit version on that laptop of Windows 7 (Assuming your using 64 bit?) with the same key underneath your laptop/PC now.