Hi Anna,<br /><br />I suppose you installed Vista first? If so, you'll need to edit Vista boot menu (BCD). You can try to do two things:<br /><br />
1. Delay the time to display the operating system<br /><br />
QUOTE:
Right click on computer >> properties >> click on advance tab >> click on settings next to start up and recovery >> edit the time to display the operating system to 10- 15 seconds >> click on apply. <br />Boot the PC you might see the xp option for you
// solution from techrepublic <br /><br />2. Download
EasyBCD 1.6 and manually add XP as second OS.