You shouldn't try tricks. You have a bootable, working "C" drive that you want to save. You will have to be happy with (live with) a dual boot.
Temporarily pull the data cable on the old IDE.
Kill the NTFS partition on the SATA with a W98 boot disk using fdisk. DO NOT FORMAT AT THIS POINT. Shut down; reconnect the IDE.
Power up, go into the BIOS to set the CD-Rom/DVD drive as first, the floppy as second, the IDE as third, and the SATA as fourth.
Pop in your XP disc and reboot. Install your "new" XP on the SATA. Make sure it does not install on your existing "C:Windows".
When you are done, at every boot-up, you will be presented with the option to boot from one of the two Windows installs. Choose the SATA.
You should make the SATA XP the default in the boot.ini file.
Locate it on your "C" root; (in Tools, Folder options, View, you have to "Show hidden files"). Right-click it - Properties - uncheck Read Only. Double-click it to bring it up in Notepad.
Right underneath timeout=30, is the default line.
It should be the IDE drive reading like this:
multi(0)disk(0)rdisk(0)partition(1)(back slash here)Windows
(multi may have 1 after it, disregard this. You're not touching that)
If you look down at the operating systems section, the SATA drive should look exactly the same, except it has the number one, (1), after the word disk. If all this is just as I say, just change the zero to one, (1), after the word disk on the default line.
In the operating systems section, add the word SATA as the first word within the quotation marks on the SATA drive line. Remember, this is the one that has disk(1) as part of it. DO NOT MAKE ANY OTHER CHANGES!
Click the upper right corner X, Save changes, and restore the read only.