you probably won't see the boot.ini file (which is in your root directory) because it's hidden.
Use the DOS command attrib to see it - go to the root directory and type
attrib -r -h boot.ini (or c:\boot.ini if you're not in the C: drive)
which unhides it and also removes the read only attribute, so you can modify it.
Then all you need to do is type
edit boot.ini
at the C: prompt (or if you're on the floppy drive type edit c:\boot.ini assuming that your default HDD letter is C
You can then modify it as you wish, save and exit. Don't forget to reapply the attributes by typing the same command as earlier, but replacing the minus signs with plus signs