Open Boot.ini with notepad after changing the "Read only" attribute.

Beneath [boot loader] change "default=" option to one of the operating systems listed beneath [operating systems] that you wish to use as the default. 

For example

"default=multi(0)disk(0)rdisk(0)partition(1)\WINNT" will boot NT from the first disk and first partition. 

where:

"default=multi(0)disk(0)rdisk(0)partition(2)\WINNT"  will boot NT from the first disk and second partition.

Depending on the types of hard drives you have as well as if the SCSI bios is enabled the "multi(0)" could possibly be replaced with scsi(1).