here's the article I got the info. from, I'll let you read for yourself..
http://****microsoft.com/content/ms-hidden-files.shtml
...it has a curse word in the beginning of it, where the **** are, you'll need to replace that part with the dirty word and figure out a way to get that into your browser address bar, if you can't figure it out, I guess ignore this tip. The information is there though. I was surprised to find it out.
And yes, you're right, DELTREE could be a dangerous command if typed in by the wrong hands, but then again, so can the system file checker, so can the regedit, so can the msconfig. I'm not saying do anything you don't know about, I'm telling you about what I have read, tried and used. You could be right about using the MS DOS outside of Windows though, it might not do anything if you use the prompt from the start menu. I usually do these commands before I defragment my HD.