jayroll123, welcome to the forum! I know that you're probably interested in Pro over Home Premium, by the tone of your post.
It may be tempting, but stay away from online retailers who sells keys for practically nothing, especially eBay. A Win 7 Pro key for $10 to $25 is too good to be true, I've been burned, and at least one other here has too. These keys are most likely stolen or diverted from programs like TechNet or MSDN, and it's illegal for anyone to use them, other than the one who pays for their subscription.
What's more practical, and you don't even need to reinstall anything, is purchasing the Windows Anytime Upgrade. In the US, 7 Pro is $89.99, Ultimate is $139.99. It's a simple, 10 minute upgrade that unlocks what you already have.
There are two ways to purchase it. The fastest is from your Start Menu, type in "Windows Anytime Upgrade", w/o the quotes, it'll direct you to the Microsoft Store, you pay, you're emailed the key, usually by the time you get to your email box, it's there. Make sure that you copy that email, and save the original to your "Drafts" or "Docs" in your email box for safekeeping. And keep in mind, this key is only good to upgrade the COA that you currently have, so don't lose it. Put it in a safe place. If down the road, you don't have a backup, or reinstall discs, and purchase another, that key won't work. But it'll work unlimited times on the COA that it's upgraded from.
The other way, you may save $10 or so, is through Amazon, they offer the same deal. You have the choice of being emailed the key, or it being sent to you.
After purchasing & receiving the key, go back to Windows Anytime Upgrade, and select the option to enter your key. You need to be connected to the internet during this time, as you'll receive some updates. None of your files or programs are changed at all.
I highly recommend this option, this is how I upgraded myself. Plus, you're not taking the chance of obtaining a pirated key that may work for a few days, weeks or months, then one day you'll have a black screen, with a "non-genuine" notice in the right corner of your screen.
When many customers pays the OEM an extra $200 for Pro, this is what they're doing, for this reason, I don't recommend adding Pro to the purchase, but do it your self, and upgrade your RAM with the difference, or pocket it.
It's really simple to do.
Best of Luck,
Cat
