Using a 2.8 GHz C2D iMac, this is how I set everything up:
Note: rEFIt is not needed for this method to work.
- Install Mac OS X to the internal drive, purely for Boot Camp management purposes
- Make main Mac OS X installation on external drive
- Boot to internal, partition drive for Windows (MAKE SURE YOU LEAVE ROOM FOR UBUNTU!)
- Install and configure Windows Vista normally
- Install Ubuntu inside Windows using Wubi, since Mac won't boot from the Ubuntu 9 CD
- Boot into and configure Ubuntu
Note: rEFIt is not needed for this method to work.