Strange... I was asked this one yesterday.
Boot with the XP cd and press R for the Recovery Console at the prompt type in
and hit enter
When the Windows installation is located, the following instructions are displayed:
Add installation to boot list? (Yes/No/All)
[Type Y in response to this message.]
Enter Load Identifier:
[This is the name of the operating system. Type Windows XP Professional or Windows XP Home Edition.]
Enter OS Load options:
[Leave this field blank, and then press ENTER].
After you perform the preceding steps, restart the computer, and then select the first item on the boot menu. This should allow Windows XP to start normally.
After Windows XP has successfully loaded, the Boot.ini can be modified to remove the incorrect entry.