The Escapist has a short article up on methods to combat various forms of motion sickness sometimes related to video gaming.

Bungie fans will recall some of the problems fans had with the XBLA version of Marathon:Durandal that caused motion sickness in some players. It was speculated that the problems were related to the field of vision and framerates being different between computers from the era in which M:D was originally developed and the Xbox 360.

In short, the suggestions are: sit further from the display, have some ginger, and just grin and bear it-- the effect can lessen with time.