I'm not sure why GOG installed the DOS version of Descent 2 under DOSbox. I run the Windows 95/98 version just fine. Thankfully, it is possible to enable the Windows version using the GOG install.
Within the Descent 2 directory, you'll find DESCENT_II.gog which is really a Disc Image that can be mounted with software such as Daemon-Tools (or possibly burned as an image onto CD but I've not tried that)
Anyway, once you have mounted or otherwise have access to the contents, within the D2DATA directory is DESCENT2.SOW. That is an ARJ file (with a different extension) which should be able to be opened with anything that supports ARJ (such as WinRAR or 7Zip).
Within that Archive, look for two files, DESCENTW.EXE and IFORCE.DLL. Extract both of these to the Descent 2 directory. Then, with the DESCENT_II.gog file mounted with a Virtual CD Emulator (Such as Daemon Tools, Alcohol 52/120, Virtual CloneDrive, etc.) you can run DESCENTW.EXE for the original Windows version of D2.
You can also Download D1X/D1X-Rebirth and D2X/D2X-Rebirth, which I recommend which are updated versions based on the Released Descent and Descent2 source supporting higher graphics, Windows, Mac, Linux support, improved multilayer, OpenGL acceleration, etc. They would still require the original Descent and Descent 2 level game files (all of which are in the GOG Descent and Descent 2 directories).
http://www.dxx-rebirth.de/?Welcome
Either way, this provides several alternatives so that people don't have to run them under DOSbox and probably resolve some of the issues people may have. (Of course standard disclaimers apply, I nor GOG should be held responsible if this trashes your system, and I'm sure is completely unsupported by GOG) :o)

descentw.exe didn't work in vista64. must be a 16 bit windows program or something. The dx rebirth is really awsome though. I would recomend it to anyone.

I haven't tried it under my Vista 64 partition yet. You also copied iforce.dll too correct? Have you tried compatibility mode?
It does appear to be a 32-bit EXE for Win95...
$ file DESCENTW.EXE
DESCENTW.EXE: MS-DOS executable PE for MS Windows (GUI) Intel 80386 32-bit
I will have to test it tomorrow.

Update: The Descent_II.gog needs to be mounted with a virtual CD-ROM (such as daemon-tools or Alcohol 52/120 for it to run properly.

Actually it said it was incompatable with my version of windows. The only time i've seen this is when it is a 16 bit program (which is not supported in x64).

Well, this is my first experience with gog.com and I would have to say even at $6 this isn't worth anything...
You are 100% correct. Why didn't they install the actual windows edition of this game and not go through dosbox? Second, why didn't they include the d2 rebirth package in this? Third, if I'm going to have to configure the whole game to get it to work without crashing (which the DosBox edition does on me) using the above to features... what did I pay for again?
I have long since been annoyed with configuring my old games to work, I figured at the price of $6 to have it work correctly and not worry about that it would be worth my time.
I was wrong. Pretty much I paid $6 just to access the .gog file and tear out all the important stuff so I could make my own, good, solution out of the pieces.
Is every gog.com game this full of BS?
Freespace 1 and 2 is opensource and after a bit of tweaking works great. I though gog.com would be the buffer between manually doing it all yourself the hard way. Guess I was wrong.

I'll admit the DX rebirth would have been nice, but regardless $6 for 2 classic games is a good deal. Consider nintendo sells n64 games for $10 and SNES for $8 and Descent falls in between the 2 AND your getting 2 games not one.

Listen people,
your anti GOG rants are utterly pointless, because you can plug D2X-XL (many new effects) or D2X-Rebirth (vanilla Descent 1/2) on top of your legally obtained Descent installation and play Descent 1/2 in full hires on 32 bit Windows, OS X and Linux. No need to complain, the original Descent 1/2 versions look horrible on today's hardware anyway.
Why should GOG pay for Rebirth or D2X-XL when they're free? And why do you complain they didn't sell them when you can get them for free?
If you don't mind having colored light, high res textures and models, smoke and gun effects and what not, give D2X-XL a shot (www.descent2.de). ;-)
So stop whining and start downloading! :-)

To continue what karx said, look up at the top of the page. What word is under GOG.com? Thats right, Beta! In other words, things may not work perfectly. Most games for most people work fine, but some have problems. Also, if you are playing on Vista x64, that version of Vista broke even more stuff for security than the x32 version did. Finally, there is always going to be someone who has problems just because GOG cannot test every possible system configuration for incompatabilities with the OS, drivers, security software, etc. and different combinations may react differently. A PC's customizability is also its curse.

You are entitled to your opinion, but I have found GOG to be a treasure chest. They still seem to be tweaking a few things, but I have very few complaints. I have made several purchases, many of games that I already owned from when they were new releases (such as the Descent Series) and have found that rebuying them on GOG is worth it for me for the convenience, additional content, etc. And then made a personal bundle of that with D2X...