How can I turn a primary/slave HDD to primary/ master

Hello, I have two hard disk drives. Each has a different installation of WIN XP. As the master (C:)is small and old enough, I want to make the secondary(F:)into primary, remove my previous C hard disk and add a new one as a secondary.
I have tried but the system don’t boot (ntldr is missing).
Is there a way to do it without mess up the set up of my present F hard disk? Is there a way to keep the F even if the hard disk is the primary? (everything in regedit is set with F:\..)
Any comments would be very helpful.
Thanks