"I would like to install XP onto the F drive, keeping the original C drive intact, until I have the complete set-up on F drive.
To do this, have I got to physically disconnect the C drive?"
Either that or disable the drive in the bios. If you don't you will create a dual boot system with essential files on the C drive.
" (2) does the main operating system drive have to be plugged in to Sata 1 or does it not matter, which socket you use. "
Usually it does not matter. You can change the boot order in the bios to match which hard drive.