I bought the game recently from GOG, and now have it running under Linux with GemRB. I cannot figure out how to equip melee fighters with their weapons for combat. My paladin keeps trying to attack goblins with his fists and not his longsword :(

I've been looking for the manual expecting to find it in pdf format in the main program directory, but no luck. My internet connection is poor at the moment and none of the gameplay videos on youtube play.

Where should I look next?

The manuals for all of the Infinity Engine games sold on GOG are downloadable extras. You should find it in your games library along with the game itself, and you've got some other extras too. Clicking on a game in your library gives you a drop-down interface with all downloads relevant to that game.

Also, there's a separate forum section for Icewind Dale, just so you know. This is the Baldur's Gate section. There's a ton of stuff in common between the two series, but you should be able to find advice more specific to your game here:
http://www.gog.com/forum/icewind_dale_series#1418131536

Great, thanks!