This is great to know - thanks, ironmanjt.
I'll be attempting the same in a few weeks. Ironically I had just emailed that same agency (DNATA) yesterday - no response yet, but maybe there's a way I can at least reserve a seat prior to arrival in the region. (Probably not, but worth a try.)
I'm also trying to visit Afghanistan on the same trip with these guys:
http://www.flykamair.com
We'll see how both visits turn out soon enough.