It depends on what operating system you're using. Here's a general install guide:
http://gemrb.sourceforge.net/wiki/doku.php?id=installation

The forums have a lot more information, especially for portable platforms:
http://forums.gibberlings3.net/index.php?showforum=91

The config file mentioned the CD's location. With gog there are no CD's. So how do we setup the config file for gog release?

EDIT:

Ok I see you just have to point the CD's to the data folder in the install location.

I've used GemRB for my old disc collection and must say that so far it runs better than it did under Wine. Great project!

I also like how they have a few of the features that BG: EE wants to implement. I think I'll stick to the open-source version :)

That's exactly what I'm wondering about the viability of BGEE. Hasn't GemRB made it obsolete already, even before release?

Mind you I haven't even tried GemRB at all, so I don't really know from experience whatever shortcomings it may have, but on paper BGEE doesn't seem to offer anything on top.
I would appreciate if anyone that knows more about the subject offers an opinion, after all I haven't made up my mind about supporting BGEE or not. :)

Well BG:EE does have the reworked graphics and new quests, but then again GemRB has icewind dale and planescape torment...

The vast majority of people that would/will buy BG:EE have never heard of GemRB and even if they had probably wouldn't want to be bothered with it.

Plus, GemRB on an iPad, from what I have read, isn't particularly well done, where as BG:EE will have an interface on iPad that is specifically designed for it.

As far as I know the graphics are minor improvements, since the original art assets were lost so they are stuck with the low res (by today's standards) graphics of the original game. Literally the only improvement is the inclusion of 1PP v4 in the shipped product, afaik.

As for the quests nothing I saw was really worthy of attention.
Only the engine improvements (instant save-load), better GUI and zoom function piqued my interest and those are (or could be) in GemRB already.

While both valid points I saw quite a few modders, some involved in "must have" mods, expressing excitement about BGEE. And they know about GemRB only too well.
Bit puzzling coming from them. Anyway we will find soon enough if it's worth the hype.


PS In case I sound like whining or advertising, that's not my intention. I'm just trying to find the merits of both projects.