Yes this is a problem related to Nvidia Graphics, you will find if you set your AA to 4X and I think 8x, the problem will be resolved.
However saying that, I recently upgrade to a XFX 8800GT 512MB, with the latest drivers, I also installed the latest version of 'Nhance' a Nvidia enhanced graphics tunning interface, and I only use that to set my graphics settings, I do not use the default interface installed with the Nvidia drivers, since this I can now set my AA to the highest level, the only issue is, you need to select the 'Combined' setting for AA in Nhance or else you will see no AA in game at all.
Wayne
