Umm, if you're trying to multi-boot from multiple disks, there are several things that can be done, but some details would help:
First, if one's dealing with Windows NT/2k/XP, the file that controls what options show up on the boot menu is boot.ini. In this case, if the other option isn't showing up there, you might be able to manually edit boot.ini on your boot drive. This would be the drive that has ntldr, boot.ini, and bootsect.dos (if you have an older system on there).
In editing this file, you need to be careful as to the syntax used in specifying the drive you want. It does not follow the partions (as you identify it yourself). I'd have to look the syntax up again, but on my boot.ini file for instance
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /NoExecute=OptIn
C:\="Unidentified operating system on drive C."
You'll notice that it's following the pattern of finding the disk, then the partition number on the disk, etc. For a second hard drive, one of those values which are 0 above will be 1. I'll have to look to see which it is. BTW, don't delete your own entry from it, just append a new entry. This way if something goes wrong, you can still use the entry in there to boot your OS up. Also, if you copy ntldr, bootsect.dos, boot.ini (and there could be one other file, depending on whether you have your hard drive controller driver in here, though it gets renamed) to a floppy...then you could use the boot menu from the floppy (rather then the HD) to boot NT/2k/XP also...
Look here
http://www.computerhope.com/issues/ch000492.htm
To specify the second hard drive, change rdisk from (0) t (1)... BTW, if you're careful (and don't delete the entry to boot your OS already), you can just edit this in notepad. There's an option to view hidden files in My Computer and Windows Explorer...
Another option is a boot loader program like System Commander, or the like...