I used iPC osx86 10,5,6 distro so dont know if it works with others.

1) have already installed leopard.

2) make another partition (atleast 25 GB or vista won't install)

3) boot into leopard. Go to disk utility and format that partition fat (ms DOS). (dont know if this is necessary.

4) install Vista. U will need to format partition again.

5) boot into vista check if everything is working and then put iPC dvd and restart.

6) Boot into iPC dvd and press next/continue choose your old leopard partition, go until customize button. Press it. uncheck all of the flags, and then chameleon boot loader only will be installed again.

7) after installing chameleon boot loader u have ur old leopard boot screen, before leopard starts press f8 and u can choose, VISTA or Leopard.