It's been a long time since I played DD, but here's what I can dredge up from the depths of my memory.
George is the merchant in Aleroth, right? In which case, did you agree to get the plant for him? I think I'm right in saying that he gets stroppy about trading with people who won't help him feed his habit.
Or do you mean you are having problems actually doing it? When you talk to him, there should be a trade icon on the left hand side of the dialogue box (looks like coins and a purse, or something like that), or a dialogue option to 'see your wares' or words to that effect. Clicking on either should get the trade window (also allows repair and identifies). You just click on what you want to sell, and what you want to buy, and then click on the scales for whoever's currently got the lower value to balance things out and then just hit the tick.
If you didn't mean either of those, then please explain further and I'm sure we'll be able to help between us.
