Can you install multiple OSs from partitions on ext HDD?

[powned]

Im doing my nut trying to work out if this can be done.

I like slipstreamed installs so I have tweaked, updated and trimmed versions of xp, vista, w7 on disks/usb pen drives ready to install.
What i hoped to do is create partitions on my 2.5 external HDD for different operating systems, then i'd like to be able to boot into an install for my chosen OSs.

Can anyone point me to any tutorials or put me out of my misery?

Cheers

 

[powned]

Id like to have some kind of menu enabling to install my chosen OS from my 500gb WD HDD, basically i just dont want to have to lug disks and multiple pen drives around with me.