Windows 7 won't boot after erasing an old HD

You're welcome. Glad to help. Stick around and learn, then help others.

None of the other forums even try to do these kinds of operations. We've been doing this and even more 24/7 for four years.

That PW disk is one of the most valuable tools we use here. Here are just two examples of the cool stuff it can do:
How to extend partition easily with partition magic – Partition Wizard video help.
Partition Wizard Move/Resize Partition Video Help.

There are many other ideas for improving your setup in the Clean Reinstall tutorial.

Yeah I will. The only other forum I've seen help like this is the Ubuntu forums. Their community is great and, as far as I can tell, so is this one.

I've lurked around here for some problems before and this place has been pretty helpful! Its just so surprising that Windows would install boot files on an old hard drive that you might remove/delete in the future..

It is the way which the installer can configure a Dual Boot at the same time it installs. It actually updates the Boot files on the existing OS drive or boot partition so that it has none onboard the partition you've just installed. So if you want to remove the older one you must write the System boot files to it first.

We developed this workaround for literally thousands of those who migrated to Win7 by setting it up in a Dual Boot with XP. Many wanted to get rid of XP in hours or days.

In your case with separate HD's, had you unplugged the other one you could have had the Win7 boot files onboard its own boot partition, then booted your choice of OS HD via the BIOS default HD or Boot menu key at boot. We advise this in advance to make it easier to remove one.