Yes, not a problem to install XP on the other drive too, just in case the main one fails/won't boot - exactly what I've done.
I feel this is safer than drive-imaging, as restoring the image is less guaranteed than having a drive with a fresh OS already installed & ready to go. There's a free boot manager like this click here you could use too.
If the drives containing the OS are of different types, i.e. IDE & SATA, you don't even have to use a boot manager. Just set your main drive to boot first in the BIOS - this is the setup I have. G