FAO Tech Nerds: Can you install multiple OSs from partitions on ext HDD?

Hey all...
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. Installing 1 OS from a USB flash is quite easy to setup but this is taxing me

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

Cheers

I can't help you with the partition questions of yours but I've been thinking about putting an os on my external HDD, how do you do it? any tutorial you can link me to please?

So, do you want to be able to select a different os everytime you boot up using one external hdd? Is that what you're asking?

via usb it going to take 5 minutes to boot
anyway u should find what u want here
http://www.ubcd4win.com/

yes. you will need the grub bootloader to do it (linux). Or i they are all windows, you will need a computer that has a bios that will boot usb drives. Grub is the best way to do it but it has a learning curve