If your bios doesn't recognize the card, you are out of luck. A bios update might fix it.
The SATA controller you bought has to be able to be bootable in order for it to work. If so, it should have come with drivers. Your dilemma is that to get the sata card to be recognized at boot time, XP needs reinstalled. During the installation process you need to use F6 to add 3rd party drivers, i.e. your sata drivers. the you can boot from sata. Anyhow, check the manual for the sata controller. It should tell you if you can make those ports bootable.
@cl-scott: I think you are misinformed or are thinking of different circumstances. Xp doesn't use this as an anti-piracy measure, it was just not a consideration in the design of XP at the time. Just like they made Xp use floppies to install 3rd party drivers. Who the heck has floppy disks these days?