First install XP on the IDE drive, with the SATA drive disconnected. Ensure it is working well & you have all the recommended Win updates installed via click here.
Then with the IDE driver connected, attach the SATA drive now & install Win7 on it, making sure to choose the correct drive/partition it gets installed on. The latter should be taken care of by default, but it's always good to doublecheck.
The Win7 install will automatically take care of the 'dual-boot' options & display a selectable choice of either OS at startup.
You can then fine-tune these bootup choices depending on which OS you'd like to load first by default, how much time you'd like the choices to display, etc. We'll come to this later if & when required. G