That the HD is SATA makes no difference. For multi-booting
Windows XP with Windows XP, check the Groups.Google.com
archives for the mid-November thread titled "Multi-boot Windows
XP without special software" by Timothy Daniels. The method
described leaves you with the option to choose between resetting
the BIOS or using Windows XP's multi-boot feature to choose
which OS to boot. (It also appeared in the newsgroup
comp.sys.ibm.pc.hardware.storage in addition to a couple
microsoft.public.windowsxp.* newsgroups.)