Whenever I run the executable, it shows up in my task manage as bogging down 50% processor... but never comes up. I've tried everything I can think of in compatibility settings, but nothing works.

Are you running the vanilla GOG installation or a source port?

My first thought is that you might be trying to run descentr.exe directly which I don't believe will work on a Windows 64-bit platform. The vanilla installation uses DOSBox which is actually what should be invoked with the appropriate conf file that's part of the installation.

If you're running a source port, like Rebirth, maybe it isn't finding some particular game resource, but I suspect it would complain as opposed to hanging as you describe.

Descent 3 should not be run through DOS BOX as it's a windows app. You should be running MAIN.EXE

Also, make sure you run it as ADMIN. Try running it in XP Compartbility Mode.,

I am running the direct download from GOG. downloaded it directly from the site and installed it no tweaks no other downloads. it just will not run. the GOG installer sets it to XP Compatibility mode by default and I have tried admin mode as well. same thing. It runs the process in the background, takes up 50 MB of ram... but never opens.

I dont'have the copy from GOG since I have my original D2 Cd's from 1999. There should be no tweaking done to D3 since it has worked fine on XP/VISTA and WIn 7.

I run it on Win 7 64 bit without issue. What if you unchecked the Compatability mode on the shortcut?

Wow, I must have missed the "3" part of the subject entirely! I also have Descent 3 on disc and have run it on WIndows 7 64 bit without issue on a machine with an nVidia GT 240. On the other hand, a second machine with a Radeon 4850 required some command line tweaking though I don't remember exactly what I did. Here's a list of options you might try:

http://www.dateiliste.com/en/descent-3/67-getting-started-with-descent-3/524-descent-3-command-line-options.html?showall=1

Fairly certain I disabled the intro and specified a resolution, but otherwise I'm not sure.