First off: Welcome to GOG and the forums!
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Interesting.
Glide is the old 3D graphics card that games used to use all the time and are no longer made. However, you can download a glide emulator from a variety of sources. GOG uses them on a variety of games that require it. They don't use it on FS2 since the game doesn't require one, though it does improve the graphics with vanilla FS2.
It is easy to install, you usually just put the files glide2xx and glide3xx into the game folder (or you computer system directory, but better your computer's folder) and you should be able to select the glide option.
GOG used to use a different glide wrapper, now they use nglide for a lot of their games:
http://www.zeus-software.com/downloads/nglide It is free to download.
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The other option is to download the Freespace 2 open source engine. It totally modernizes the game and makes it look absolutely stunning (as well as play nicely with modern Mac, PC and Linux OSes). There are also a lot of mods that you can get for it.
It requires the retail or GOG version of Freespace 2 (which you have), but after tha you download this on top of the vanilla version and it makes the game much nicer, especially if you download the modernized game assets. This is a community driven project and is free to download. If you are on Windows, it also requires you download OpenAL.
A GOGer put together some instructions which can be found here:
http://www.gog.com/forum/freespace_series/quick_and_simple_freespace_2_scp_installation_guide/page1 They are slightly out of date as while the assets are still 3.6.12, a new engine has been released, 3.6.14.
More links for manual installation instructions can be found here:
Getting started Windows installation These are slightly more up-to-date. The automated installer which used to work is no longer available anymore. However, the manual installation is not that bad.
Here's what the game looked like as of last year with the open source engine (even better now):
http://www.youtube.com/watch?v=xhAR8rWPluQ -------------
Out of curiosity what is the resolution of the respective monitors (e.g. 1900 X 1200)?