Ext. USB HDD (boot)

It occurred to me.
Example :
I have 320GB ext. usb hdd, so, can i partition it with 3 partitions.
First & second with boot (multiple boot), first with win 7, second with XP and 3rd i would put apps for installing when windows is installed.
Answer #1
That’s a pretty good idea, but what exactly do you need help with?…
Answer #2
Why go to all that trouble to have a slow operating systems ?
Google “installing OS on external hard drive” if you need to know more..
Answer #3
))) OMFG
sorry……..
I am installing for my friends and family windows etc……
so, i want to create multiple boot with win 7 and xp, when i connect ext. hdd to clean PC, so i can choose which OS to install to clean pc.
Same thing like u can DL dual or triple or multiple boot options on DVD, u put DVD in dvdrom, boot from dvd in bios, choose which OS to install, same thing but with ext. hdd