Booting from an external drive depends on support from the BIOS on the motherboard.
For some systems, you will need to boot from a floppy and load the drivers for the external drive.
My preferred solution is to install a "hot-swap" drive bay.
The bay installs in a 5 1/4" bay, and has a removable tray that you can install a hard drive into.
Simply have extra trays for each OS version that you wish to boot to, and install the appropriate tray into the bay and boot up.
I get mine from www.compgeeks.com for around $7 US each.
Now, a caution:
Unless the hardware is IDENTICAL on each system you will have problems trying to use 1 set of drives for each PC.
For Windows NT, W2K, and XP, any PC that does not match the original hardware may not boot at all.
Further for XP, you WILL generate a product activation event when you move the drive from the PC where XP was originally installed to a different PC. Even if the PCs are identical.
If you want more suggestions for multi-booting, please post a new question detailing what you need to accomplish with your multi-PC multi-OS boot setup.
Chas
