Can't Delete old Vista Windows installation folder in Windows XP

[mang]

I cannot boot a Vista Box so I installed Windows XP in the Same C: drive but under separate folder C:\WINXP\Windows\ the old Vista installation Files are in C:\Windows\. Now boot into XP i cannot delete the C:\Windows\ folder , when try to delete a dialog appears Cannot Delete 'FXSEXT.ecf' how do i delete the Vista Folder which i no longer use ?

 

[dashing.sujay]

^Use unlocker, but do note the service which Vista folder/files are using.