That's simple enough, I think.
I assume that the GOG's version is the latest patched version, right?
Well, now, what unofficial patch should I install then?
And could you please give me a link to those patches, given that arcanum-terra is down?
Yes, GOG's version is patched to version 188.8.131.52.
The patches you need and order to install them is:
1. Unofficial Arcanum Patch Version 091225
2. High quality townmaps pack
3. Arcanum High Resolution Patch Version 1.1a
4. High quality music pack (MP3)
If you are running Vista, Win7 or Win8, either install Arcanum (you really should do this to all your games, saves you from tons of headache later) outside program files folder (c:\games or something) or run the patches as administrator to make sure they install properly (right click the executable and select "run as administrator").
Also right click the arcanum shortcut, select properties and add "-no3d -doublebuffer" to the end without " ". (should look something like this C:\games\GOG.com\Arcanum\Arcanum.exe -no3d -doublebuffer)
You can find Unofficial Arcanum Patch and High Resolution Patch from my site
(downloads -> arcanum). Most others mods made by drog can be found there as well but I don't have space for Arcanum lossless soundtrack (WAV), High quality townmaps pack and High quality music pack (MP3) so you need to get them from Terra Arcanum downloads section
Edit: added mention of Win8 as that abomination now exists
Edit2: Most important Arcanum mods and files are also available on my OneDrive account
). There are also some working mirrors on Drog's site