Clean XP install without deleting existing XP OS

I want to gradually do a clean install of XP while retaining the use of my existing XP installation until I am completely happy with the new.

I have 2 hard drives in my Dimension 9150 and would appreciate help as to the best way of achieving this. I don't really want to keep on swapping the hard drives over or removing one of them. Also would like the clean install to initially ignore all the usb peripherals (except keyboard and mouse) I have connected without physically having to unplug them everytime I want to work on the new install.

Any suggestions much appreciated.