The installer is not necessary. The game files are in the "/gnome/" folder on the original disc.
You can just copy them elsewhere. You will need a registry key to point at your CD drive still - there is documentation on the internet how to create those registry keys. Here is a technical description of the changes GOG.com made
, although it primarily is a no-CD patch.
The synchronization patch is not too important as you can run the game with a different thread affinity. Such stuff is documented on the vogons forum if I remember correctly. The resolution patch is probably the most interesting bit, although it is not necessary if you use software like dgVoodoo (mentioned below).
The GOG.com version also includes the open-source software ipxwrapper
I don't currently remember, but I think the GOG.com version also comes with DxWnd
Other users on the forums reported using dgVoodoo 2
instead of using the patches supplied by GOG.com.
So really, the GOG.com version (at the moment) is just a collection of already existing software.
The primary reason for buying the GOG.com version would be, that it is already prepacked/installed for you.
Additionally you can get official support (or money back) and there might be more patches for GOG.com users in the future.
It's also great to have a legal source for this game.