The easiest way to dual boot is to use a third party boot manager.
GAG is a free boot manager that will allow you to use 9 different operating systems installed.....GAG installs in the 8MB lead in on any hard drive and then protects the MBR of each operating system installed on the computer so that each and every operating system full integrity remains intact...unlike microsoft's boot manager that overrides all previous MBR.
There is no need to have to overwrite the boot sector.
GAG, the Graphical Boot Manager