When booting up to Windows XP you may get an error that reads: Unmountable Boot Volume. 

This is probably because your boot.ini file is messed up. Here is a possible remedy: 

1. Start Windows XP with the Windows XP CD in your CD/DVD drive.

2. Once you see the "Welcome to setup" message, press the letter 'R' on your keyboard to enter the Recovery Console.

3. Select the Windows installation to be repaired (you will need to know the administrator password.

4. You will then get a DOS prompt. from here, type: chkdsk /p  [Enter]

5. When that is done type: fixboot  [Enter]

6. Type: Y at the next prompt  [Enter] 

7. Then type: exit  [Enter]

8. The system will now reboot into Windows.

If for some reason that didn't work, you can boot to the recovery console (example above).

Type: "chkdsk /r"  [Enter]

When done type: exit  [Enter].

This takes a bit longer, but the system should boot back into Windows.