How do I boot windows XP in virtual box into repair mode?

Solution 1:

Windows XP did not have a built-in repair environment. (It had none of the current "servicing stack" improvements that were introduced with Vista – there was no DISM yet, the installer was .cab-based.)

The closest thing available is the "Repair installation" option in the Windows install CD – after the initial "To install, press ENTER" screen, you can select an existing Windows folder and have the installer try to repair it.

(After this is done, the system will probably be at whatever version the CD contains, so you will most likely need to re-install every single update.)

However, if you can get into Safe Mode, you can instead try rolling back to an earlier "System Restore Point" snapshot (which is available through Start > Accessories > System Tools), which will roll back OS changes while preserving your file changes.