I found this in a few different places around the 'net - hopefully it's helpful:

Modify Boot.ini

Windows XP uses the Boot.ini file to determine the operating system options to display during the startup (boot) process. Boot.ini is set with the hidden and system file attributes and flagged as read-only by default.

Have you been changing Boot.ini lately? Are you tired of opening Folder Options, and clicking Show hidden files and folders on the View menu, so you can see Boot.ini in Windows Explorer? Or worse, did you forget to remove the read-only attribute before editing the file?

You can use the command-line tool, Bootcfg.exe, to quickly edit your Boot.ini file. You can modify the timeout (the amount of time Windows waits before choosing the default operating system), and add additional entries.

• Click Start, click Run, and then type cmd.
• Type bootcfg.exe
• Check out bootcfg.exe /? for more options.