Despite already owning Descent 3 + the Mercenary expansion, I had to try them from GOG because of the guarantee that they would work with Vista. I could not for the life of me ever make Descent 3 run reasonably well in XP, let alone Vista.
The installation was smooth, and the game runs flawlessly, so I'm extremely grateful and now a huge fan of the service.
Thank you!

Descent 3 works wonderfully, but I cannot get Mercenary to run, it gives me a "cannot load merc1.d3l"

I had the same problem until I searched on google and found the following url:
http://www.planetdescent.com/asp/forum_posts.asp?sectionid=3&forumid=10&topicid=1331
I renamed merc.hog to extra.hog and then it worked :O

You are a wonder!!!!!! THANKS!!!!! you don't get to see the Mercenary movie, but you do get to play it. IT WORKS!!! You get a point form me! :-)

Thank you and you're welcome, I'm always happy to share things like that :)