Exactly what do you want?
do you want to have xp home and in another hard drive xp pro and when you are using xp home let's say you don't want to even see the other hard disk.(with the other installation of xp pro)
Or did you just meant that you do not want both WIndows in same hard drive.
If you want you can also get some help at microsoft site and search for
dual start up and things.
I can give you some tips too but need more info.