Hi Peter,
What I think has happened is when you installed Jaguar it set up the system to boot from that partition by default. If you have your partitions set up anything like I have mine... then resetting the PRAM will do the trick and tell the computer to look in your bootloader partition first (which should be the first partition on the hard drive), instead of the Jaguar partition.
Let me see if I can find the article on YDL's web site for you, it will be much better at explanining what to do.