The official Battlefield 1943 twitter page has updated to reveal that you can use the semi-auto rifle, sniper rifle, or SMG from Battlefield 1943 in the forthcoming Battlefield Bad Company 2.
If you don't believe us, check here. It says:
"Think you're a Bad Ass with BF1943 weapons? What if I said you'll be able to use your Semi-Auto Rifle, Sniper Rifle, or SMG in BFBC2!"
See? We weren't lying.
Battlefield: Bad Company 2 is out for PC and high def console in Q1 2010.