This guide will be directed toward Ubuntu users, but it should be applicable to most Linux distributions. All of the applications listed (except GemRB) can be installed via the Ubuntu Software Center by searching for the application name there, but I will be using the command-line method, so that those using this guide can simply copy and paste.

Install GemRB
You can either install from source, or use pre-compiled packages. We will be doing the latter.

1.) Open a terminal, and execute each of the following lines separately:
sudo add-apt-repository ppa:sao/ppa
sudo apt-get update
sudo apt-get install gemrb

Install Your Infinity Engine Game
There are a few ways to install the game for use with GemRB, but in my opinion, the easiest is to use with [url=http://www.playonlinux.com/]PlayOnLinux as the front-end. If you wish, you can just install Wine (sudo apt-get install wine) and use it, but you may have to do more configuration.
1.) Install PlayOnLinux
sudo apt-get install playonlinux

2.) Install Baldur's Gate II using PlayOnLinux
*Launch PlayOnLinux and click "Install".
*Select "Games" on the left, and find "GOG.com - Baldur's Gate II Complete". Select it and click "Install"
*It will ask if you want to download the game from GOG; select appropriately
*Click "Browse" and navigate to your setup exe file (setup_baldurs_gate_2.exe) and click "Next"
*Follow the instructions to install the game

At this point, you should have a Baldur's Gate 2 icon on your desktop. If you want, you can simply run it from here using Wine. It actually runs pretty well just using Wine, but to run it natively using GemRB, we need to do a bit more:

Configure GemRB To Use Baldur's Gate II
Copy the sample config file to your desktop (execute in terminal)
cp /etc/gemrb/GemRB.cfg.sample ~/Desktop/gemrb-bg2.cfg

*Open the file that you copied to your desktop in a text editor, and modify it accordingly:
1.) Find "GameType" and set it to "bg2"
GameType=bg2

2.) Find "GameName" and set it to "Baldur's Gate 2"
GameName=Baldur's Gate 2

3.) Find "GamePath" and set it to where Wine installed your game. PlayOnLinux defaults to the following:
GamePath=~/.PlayOnLinux/wineprefix/BaldursGate2_gog/drive_c/Program Files/GOG.com/Baldurs Gate II

4.) Delete all "CD" entries except "CD1". Set CD1 to the BG2 data directory:
CD1=~/.PlayOnLinux/wineprefix/BaldursGate2_gog/drive_c/Program Files/GOG.com/Baldurs Gate II/data

5.) (Optional) change resolution
Width=1024
Height=768

6.) Save the file.

Run The Game!
Now the fun part...running the game.
1.) Execute the following from a terminal:

gemrb -c ~/Desktop/gemrb-bg2.cfg

That's it :)

Hey thank you so much for this! One problem; I change my screen size but all it does is change the size of the box that it runs in, not the actual game itself. Any way to fix this?

Thanks!

Request for this thread to be stickied...

You still need the / a widescreen mod if your desire resolution is not originally supported
http://www.camagna.net/g3mirror/index.html

As tomty89 suggested, the widescreen mod is still needed to support resolutions other than what the game supports. However, I have noticed that the widescreen mod is a bit flaky with GemRB. GemRB may have since been improved though, so please check the GemRB site for the latest updates.

Just two things to keep in mind.
GameName is completely arbitrary and does not need changing (same for other CD paths).
Oliver's ppa has an old gemrb version currently, so better get a .deb package elsewhere.

Out of curiosity, would gemRB be able to run the patched and combined BG1 & BG2 setup outline here: http://www.gog.com/news/enhance_the_gameplay_in_your_edition_of_baldurs_gate_from_gogcom ?

EDIT: Nevermind, the answer is apparently yes :D (Just using the BGT WeiDU 1.15 mod and the latest git build of gemRB, compiled on Ubuntu 12.10 x86_64), seems to run very well with the exception that I was 'waylaid' on the way to the Friendly Arm and my characters got stuck in an infinite battle against a load of invisible wolves, bandits and hobgoblins.

Steps I took documented here: http://www.thumbnail.org.uk/cgi-bin/archive/post/1359038341

Thank you for this excellent guide!

A couple of additions:

If you put the gemrb.cfg in ~/.gemrb/gemrb.cfg, you can run gemrb without any additional options. You might also want to set your cache directory to something like ~/.gemrb/cache (create the directory first).

Sorry for dragging out this old thread, I was just wondering about this point. Any idea where I can get a newer version?
None of the links on the download page on their website work, and the last official binaries on their sourceforge page are versions 0.3.0 from 2008 (and for i386 anyhow).

I tried compiling the source they provide on their sourceforge (lastest stable being version 0.8.1), but it seems beyond my skill level. I keep getting missing library errors (it says that at least python 2.3 is needed, but I have python 2.7.5!)

You can download v0.8.1 at that sourceforge link you gave. Just click on the link that says "Looking for the latest version?"

Do you even need to? What distro are you using. If you are compiling from source you may need the dependencies' source as well. On Debian based systems you often need to add deb-src lines to your sources.list.

I feel I am missing some fundamental understanding here. If the last binaries available are several versions ago from 2008, I would obviously need to compile the provided source code, no? PlayDeb.net's page on GemRB has an apt link, but there doesn't seem to be anything there. When I added it (through the GUI) doing 'deb http://www.playdeb.net/install/gemrb trusty gemrb', I get some NODATA error, even though it automatically generates a source version of the same (along with the binary).

I don't know what you class as source, but the content of the download looks to be a complete package to me (gemrb.exe and assorted .dll, plus other IE files) See attached image.

That looks to be one of the windows binaries, not for linux.