If the product key is on a Windows sticker, you don't even have to buy a copy of Win 7 Home Premium. Just borrow an OEM copy of the same version from a friend, or download an ISO, and install it.
This is not piracy. The license for Win 7 Home Premium is included with the machine. You just need the installation media. You may not even have to enter the key because it's probably in the BIOS. If you use a borrowed copy, use disk copying software to burn your own image file and/or disk in case you need to reinstall it later.
Before you start, go to Dell's site, search for and download all current drivers for your model. You may have to refine it further by using the part number (p/n) or the service tag.
Save them in a folder, copy it to a flash drive, and as soon as you get to the first desktop of your new installation, copy that entire folder to the Downloads folder on your machine. Then, install all of them from your own hard drive.
If you want to save some work, contact Dell's tech support. They may have a pre-made recovery disk set for your machine that can install the entire original out-of-box setup including all of the original drivers and Dell's support/update utilities and links. If so, they may sell it for as little as $20 - $30 shipped. If you go this way, be sure to update the drivers.
A final word - When you do your installation, do NOT have the machine connected to the web, even to activate Windows, until you have first installed your anti-virus and ant-spyware software. NEVER go online without full battle armor.
Good luck.
