Dual booting XP Pro and Windows 2000 Pro

I switching over to XP from 2000. I installed a new hard
drive in my machine and removed the 2000 drive. I did a
clean install of XP Pro on the new master hard drive. I
then installed the old hard drive as a slave. Both are
jumpered to be cable select. I edited my boot.ini to add
the 2000 drive as a bootable OS. Everything worked
perfect. I got the menu at start up to select the OS that
I wanted to runn and they both worked. I then booted to XP
and downloaded SP1. After it installs the machine will not
boot 2000 anymore. I made the 2000 drive the master and
2000 boots, but XP will not. What is going on? Can someone
help?

Thanks........

Dual booting XP Pro and Windows 2000 Pro