I understand about lack of resources, it can totally cripple your civilization in the mid-game and reduce you to a third world power in the late game. My thoughts would be to claim as many SR's as you can in the mid-game...conquer cities if you have to by throwing hordes of Longbowmen and Pikemen at them (which will work even if they have musket men and you don't). Goto war as soon as you feel you can take the city and defend it for a turn or two, that or raze it and be prepped to settle yourself if you are worried about a culture imbalance. Sue for peace as soon as you get what you want...you might pick up some extras from them in the process.
Switch back to science and aim for the next resource...I think its more important to know where they are going to be before anyone else does...almost more important than actually having the resource. If you can take your opponents source and make it your own before they have the chance to use it, so much the better.
I played a game where the only resource I had on my home island (a decent size one at that) was horses, everything else had to be imported. I think that this was the most fun I've had in the game to date. I actually felt the need to form an empire. By Civ 2 standards I had enough room, enough people and enough production to do a space race victory without a problem...in Civ 3 I needed to expand somehow to get the resources...much more fun to be 'forced' to do so...I could have traded for the resources (the Germans had more resources than cities!) and gone for culture but instead I mobilized for war and took 'em!
I think my advantage in that game was running into the English early, and wiping them off of my continent (I had bowmen and well...they didn't) a low-tech war with just horsemen between us would have set my well back in the tech race...as it stood I knew where and what to take before those that lived there knew it was important.
