Actually i have this same issue EVERYTIME i need to do a powerpoint presentation at school, church, or anywhere else since not everyone is on a mac. I was thinking of just buying the VGA adapter and connecting my macbook directly to the projector. From what i hear, its software that you have to purchase that allows the pictures to convert to window's format. If anyone has an idea of how to get around this, it would be great. But if not, i'd like to know where to get that software also.
Sorry i couldnt be of any help, but youre not the only one with this issue =)