1. Make sure your partitions are in order( you need at least 3)
You need 1 partition for windows which should already be installed, you need another partition for OSX which you will install at a later time(at least 40 gigs),and then a partition for ubuntu (only 7 gigs).
2. Install Ubuntu 10.4 on the 7 gig partition.
3. Check to make sure you can still boot into windows (should be able to as Ubuntu is made to be run side by side with Windows)
4. Install OSX on your other partition (< 40 gigs)
5. Install Ubuntu 10.4 again on the 7 gig partition
6.Upon Reboot Grub should show Ubuntu, Windows, and Mac allowing you to change between them effortlessly

This is and overly simply guide if you need more help don't hesitate to askHope you'll be enjoying your new hackintosh
AJAir