Okay, so it is in fact an aluminum sleeve that I'm working with here:

http://www.bikeforums.net/archive/in.../t-533806.html

I guess it's a Cannondale thing. If Cannondale made the Slice forks with the aluminum sleeve pre-installed I'm assuming they also took into consideration people like me who would cut the steerer down a lot. Therefore I'm sure the aluminum lining goes down far enough to where I shouldn't have any problems tapping the star nut down further. I will probably just take it to the LBS and have them do this once my headset and stem get here and I know how much I will be cutting off.