Back around the launch of "Battlefield 1943," DICE promised that folks who purchased the game would be rewarded with an exclusive weapon in "Battlefield Bad Company 2." Speaking with Patrick Bach, senior producer at DICE, I was able to confirm that the deal is still in effect.
Players that purchase both games and register those games on Veteran.Battlefield.com will unlock access to the WWII M1 Garand. (The site is not yet fully-functional, so don't try it until the game launches.) The weapon is basically the same semi-automatic mid-range rifle carried by the rifleman class in "Battlefield 1943."
It would appear the unlock is tied to your "Veteran" status, which relates to how many "Battlefield" games you've registered on EA.com. Level 1 Veteran requires two games played, so you could probably attain the same unlock having played any previous "Battlefield" game (including the first "Bad Company").
In addition to the WWII M1 Garand, the WWII Thompson machine gun (carried by the assault class in "1943") and the WWII M1911 .45 pistol, will be unlocked for anyone that purchases a new copy of the game and activates their VIP access code, which we discussed yesterday.