With the supplied Microsoft tools, the only supported method is to install the MS OSes in order from oldest to newest. Since you are trying such in the wrong order, you'll need a third party tool to make this work.
It's possible to solve this with drive trays, some BIOS will support selecting which hard disk to be the boot drive, but in short, you have to write about what direction you want to go.
Often mentioned are Boot Magic (of Partition Magic fame), XOSL and after that it gets pretty sporadic what else is out there.
about a year ago, i built a computer, and installed windows xp pro on it. i recently decided that i would like to set up multi-booting so i could also run windows 2000. i got a second hard drive and a windows 2000 pro disk. when i tried to boot up my computer with it, it did not work. and i also had a windows 95 disk that i have booted with before. so just to see what the problem could be, i tried booting with the 95 disk. it didn't work either. i think it is because i run windows xp on my main hard drive, so it disables booting from any other disk, cuz when i try to boot from the xp disk, it works fine. i checked out some of microsofts help files, and couldn't find anythign. the only thing i found was a description of how to set up multi-booting, and they do say to always install the earlier version first. if there is any way possible to get windows 2000 on my computer without losing xp and the stuff i have on my main disk, that is what i want to do. any help would be appreciated.