If you cannot boot into Windows I would suggest first trying the Recovery Console:
http://support.microsoft.com/default...b;EN-US;307654
To try to fix the boot:
Assuming that your XP is on C: then:
Type:
FIXMBR C:
then enter. After that completes type:
FIXBOOT C:
then enter. After that completes type:
BOOTCFG /rebuild
then enter. After that completes type:
EXIT
then reboot.
If in the process you are asked to run
chkdsk say YES.
Also after the BOOTCFG /rebuild you will be prompted to:
C:\Windows
1. Add installation to boot list? (Yes/No/All):
2. Enter Load Identifier: (Custom description for an operating system loading from the Boot menu)
3. Enter Operating System Load Options: (that is: /fastdetect)
Reply:
1. Yes
2. XP
3. /fastdetect