I have fond memories of playing Descent I, Shareware on my 486 PC years ago. I have little experience of Descent 2 but I am told it is every bit as good as the original so I highly recommend buying this package. You can run this old MS-DOS game using the DOSBox DOS emulation software on a modern PC (i.e. XP or Vista) and the DOSBox software is included in this installer.
Alternatively you can go to the website of the Descent Rebirth project (http://www.dxx-rebirth.com/) and download a new Open Source game engine for free, which will allow these two titles to be played without DOSBox on a Windows, Linux or Mac computer. The new engine allows the original game content (instructions are provided for copying the game content from an existing installation) to be played using the modern Open-GL graphics specification allowing stunning resolutions such as 1600x1200 and effects such as Tri-Linear filtering as seen in modern games. A great new look with the same playability of the original game...
The only gripe I have with this package is that the downloaded installer must be run on a Windows system to extract the game files. There is no way to manually unpack the installer EXE file to get at the game content, e.g. to manually install on a Linux system using the Linux port of DOSBox or the "Rebirth" game engine. If you are a Linux-only user you may need to run this installer on a friend's Windows machine so you can archive a copy of the extracted game directories.