If I'm correct, been a while since I've formatted a HDD to dual boot.
Ok, simple if this correct, just partition your HDD into at "least" 2 partitions. Once thats done simply go ahead and install each OS on 2 different partitions, can be more partitions for music, pictures, video, etc. After they are both installed restart the computer and set the boot sequence to boot from the HDD then restart and it should work. Remember to give each partition your putting the Operating Systems on around 20GB at least, if not more.
I haven't dual booted in a while, year-ish, so its possible I'm wrong, but from what I can remember, thats correct.
Also to note: when you go to partition the drive, you will lose your information, unless your using a special program that does it for you.
I just read your specs, it says 40GB HDD, if thats the HDD your talking about to dual boot on, you may have problems, because of its size.