You can set the boot time in windows XP as your wish if you are install two operating systems on same computer, for example window 2000 with windows XP or more than two. Yow can do this with editing Boot.ini file. Here you can also set the sequence for operating system which operating system boot first.
First Right Click on My Computer option and then select its Properties. In next dialog box open Advanced tab button. Under Startup and Recovery, click on the Settings button. Use the spin box "Time to display list of operating systems" to set the number of seconds you want the system to wait before automatically starting the default operating system. Here you will set time in seconds and its range start from 0 and ends with 999 seconds.
After set the time, then click OK option to close the dialog box to save your change. The next time you restart, the new time will take effect.