I'm selling my better PC.

I downloaded DBAN to a cd to "nuke" the HDD, and downloaded Win7 from Digital River.

I got my windows key off of my computer to use when installing Win7.

Is this the correct procedure to do before I send it off?

Am I missing something or doing something wrong?

There is no such thing as a "correct procedure". But if you are really concerned with security, zeroing out the hard drive is the best you can do, unless you want to spend literally all day running pass after pass on the drive to make sure nothing is left, or keep/destroy the drive. But the reality is, the person buying the computer wouldn't even know where to begin to recover data, let alone even think about doing it.

Also, why give up your key for Win7? Scraqe that thing off and keep it, or charge more for the key.

I'm not giving the key away, I'm using it to reinstall Win7 after I "nuke" the hdd.

If worried about it, completely swapping out the drive is best. It's also the only 100% effective method for SSDs. Most HDDs are fine with a single rewrite.

My suggestion is swap out the drive. Simplest and 100% guaranteed.

There are people that buy PCs on ebay, craigslist, etc, specifically for data recovery. For scholarly, training, whitepaper, and more insidious reasons.

You can ask for more for the PC as-is, but you cannot keep/sell it separately it if it's a prebuilt PC's key.

You are therefore transferring the license (and by association, the key).

No matter what they tell you, OEM keys are not locked to the system. Just saying.

Ok, swapping out the HDD not being something I want to do, would DBAN get the job done?

1. Keys used by OEMs the likes of Dell, HP, etc are tied to the BIOS signature used by that company. These keys CANNOT be transfered to any PC with a different BIOS signature FULL STOP.

2. System Builder OEM keys are different. Before Windows 8, the license was explicit in that the key could not be transferred to a new PC build, but Microsoft would usually still allow it (also, strictly license speaking, you weren't allowed to build yourself a PC for... yourself with a systems builder license, as it was a violation of the TOU). Windows 8 retroactively changed both of these things due to an update to the requirements of using the System Builders license.

So you are only marginally correct, but not for prebuilts which is what I specifically mentioned.