Just for future reference. If Windows XP backup gives you the error: “error returned while creating volume shadow copy: 80042301”, do the following:

• Backup the Registry; Open “regedt32.exe” and navigate to “HKEY_LOCAL_MACHINE/system/setup”; Change the “UpgradeInProgess” value to “0” [1]; Change the “SystemSetupInProgress” value to “0”.
• Open “regsvr32 ole32.dll”.
• Open the Services MMC snap-in and restart the “COM+ Event System”, “COM+ System Application” and “Volume Shadow Copy” services.

This was lifted from here. Time to thank the google gods.