Hey buddy I have the same problem as you, except I use a 9800XT with the latest drivers. When I play the Omaha level in single player, the bunkers wouldn't show until I get to the shingle. I don't know why but I've tried differ driver versions and it's still the same. I don't have any problems playing Omaha in multiplayer.
you got the Graphics on it highest?? I think that might be the problem. My video-card is an GF4 MX440 SE, worser then yours, but i can see those bunks.