GO with Battlefield 1942!!! pretty cheap to buy now, there is a mulitplyer demo out there too. you can play single player, but it get boring really fast, multiplayer is the way to go.
for on foot you can be: a scout (sniper), assult, medic, engineer, and anti tank. you can play as the Germans, Japanese, americans, canadians, british, and the russians. you can drive heavy tanks, medium tanks, mobile artillery, jeeps, halftracks, fighter planes, bombers, dive bombers, destroyers, battleships, subs, landing craft, aircraft carriers. and there are fixed gun positions like; mg nests, mg bunkers, defguns (artillery), anti tank guns, AA guns.
A group of us have started a bf1942 clan in the off topic disusion. http://www.finescale.com/fsm/community/forum/topic.asp?TOPIC_ID=16511
we're always looking for new recruits