A+: XP's boot.ini
Boot.ini is a file n the default boot drive (even if Windows is installed on a different drive letter) which configures how to start XP, and is very specifically formatted. It can be edited by Notepad or MSConfig, or Bootcfg can revise it from wither Windows XP or from the XP Recovery Console.
The [boot loader] section specifies how long XP waits for an override command to start loading the default OS.
The [operating systems] section specifies the name to call each version of Windows on the system, and in which partition of which hard drive to find each.
Do NOT alter boot.ini unless your PC won't boot, and if that strikes, the Microsoft Knowledge Base for XP should be your first stop to look for solutions.