When booting up to Win XP you may get a error that reads "Unmountable Boot Volume". 
This is probably because your boot.ini file is messed up. 
So, what do you do about it, panic and try to mount your boot in your computer...... 
No that is probably not a good idea. 
You can boot to the XP cd and when you see the Welcome to setup press the letter R
You will get a dos prompt
Then type "chkdsk  /p" without the quotes and hit enter
When that is done type "fixboot" and hit enter
"Y" and enter at the prompt
Then type "exit" and hit enter
The system will now reboot into Windows     
If for some reason that don't work for you, you can boot to the recovery console like above and...
Type "chkdsk  /r" then enter
When done type "exit" and hit enter.
This will take longer, but the system should boot back into Windows.