I've read in the forums (from a reliable poster) that those other boards cripple the AGP slot by actually running it through the PCI bus. I've also read that they are limited to a few select AGP cards (there's usually a list posted on their sites) which can be used.
Apparently, the Asrock Dual board is the only one that has "true" PCI-E and AGP capabilities. If I can find the original thread I'll post a link here.
EDIT: Here's the thread.
You never know, he's in Bulgaria (home of the most feared Olympic Weightlifting Team in the world, go Zlaten!!) so he might me able to fetch a decent price for the old card.