Yes, you can, I've read on the forums that it was ok for all the games here in gog, legaly I mean, at long as the LAN is in your private property (i.e. not at a friends or a big lan of hundreds persons and stuff), and your friends uninstall it after, ... I guess.

Clarification: Will CD key or anything else stop me from playing a copy from GOG on a LAN?

There isn't CD Key in Unreal nor Unreal Tournament GOTY :)

thanks tapeworm and dukeniko

I don't remember which game it was, but that game had a CD key pre-inserted and didn't work online because everyone had the same cd key. It might have been sacrifice.

I'd like to know as well. The only reason I'd buy a 4 year old game is if I can play it on my LAN with my brother using the same copy. (I.e. I don't want to have to buy it twice).
I know originally, that's what it meant you had to do but hopefully that's no longer true.

My understanding is that it does have a CD key plugged in somewhere to stop you from copying it over to a friend and letting him enjoy the multiplayer in full but there's nothing stopping you from enjoying a LAN with your friends.

So we've established that it isn't wrong to play UT2K4 over a private home LAN with family, say your brother. Now supposing you have a very large family, say twenty people, would that then be a crime? Now suppose those people were actually friends, and instead of playing on a private home network, you were playing on a private university network, using the university's computers... and what if instead of buying the game yourself and giving it away to your friends for the gaming session, you bought it for a computer games society and let all the members play it at a price that was practically giving it away - as in, they pay for membership but don't have to pay any extra to play this game specifically. Would that be a crime, Bart?