Can't eject Windows 7 install disk to get drivers from Snow Leopard Install Disk
Turn the machine off.  Turn it on again, and hold down the trackpad button. The disc should eject.

http://docs.info.apple.com/article.html?path=Mac/10.4/en/mh1750.html


  Restart and hold down the mouse or trackpad button until the disc ejects.


(The other suggestions don't apply; you're not in MacOSX yet, you don't have an eject hole, and you have an Intel machine so the firmware thing won't work.)

The other Apple support page is here:-

http://support.apple.com/kb/HT2801?viewlocale=en_UShttp://support.apple.com/kb/HT2801?viewlocale=en_US