How do you install Backtrack 3 to a hard drive without wiping the data?

I have Windows Vista and Ubuntu already as boot options and I want to add Backtrack 3 as another boot option. I already have the iso downloaded. I've searched around but all the tutorials I have read don't tell me how to boot into the 3rd option (VESA/KDE) or their instructions would wipe my hard drive.Any help would be appreciated, thanks.