I installed Windows 8 on a computer of mine and then decided I didn't like it there, so I reinstalled Windows 7. I chose not to format the hard drive because I had some files I wanted to keep. Unfortunately, that kept the Windows.old directory and now I have approximately 17,000 files that simply will not delete and I am not going to manually takeown each file. Linux is also not an option.

So, am I going to have to reformat anyway?

First, go to:
http://www.howtogeek.com/howto/windows- ... -in-vista/
Second, right-click the "Windows.old" folder, and click "Take Ownership"
Third, just wait, it will AUTOMATICLY takeown ALL the files in the folder.
Fourth, delete, it might take a while to delete, but it should delete.

Can I ask why?
Also, if you don't like Linux, ERD Commander 2005's file explorer perfectly deletes Windows system folders.

There's an option in disk cleanup. Though you might have to chose clean up system files.

I don't think there is any safe way to downgrade Windows 8 to Windows 7. It's going to leave leftovers in any way...
Back up your files, do a deep format and install Windows 7.
That's what I would suggest...

I can't believe this site, it's a Google for not reading or searching. Even the moderators are getting some doubt from me now: http://support.microsoft.com/kb/930527/en-us

I hardly ever use Disk Cleanup; most times I forget it's even there.

this should be common knowledge for any beta tester but anyway run disk cleanup
Open Disk Cleanup by clicking the Start button Picture of the Start button. In the search box, type Disk Cleanup, and then, in the list of results, click Disk Cleanup.
If you're prompted to choose a drive, click the drive you just installed Windows on, and then click OK.
In the Disk Cleanup dialog box, on the Disk Cleanup tab, click Clean up system files.
If you're again prompted to choose a drive, click the drive you just installed Windows on, and then click OK.
Select the Previous Windows installation(s) check box, and any other check boxes for the files you want to delete, and then click OK.
In the message that appears, click Delete Files.

For windows XP go to all programs
accessories
system tools
and you should find it there

After installing Windows 8 build 7955, I had a similar problem. I just copied the folder Windows.old an external hard drive via Linux LiveCD and then I format the entire system disk.