how about put the hard disk in another computer (also running xp), or boot your computer into windows off another hard disk, then run chkdsk on the problem drive?
alternatively, use a disk maintenance prog boot cd (partition manager perhaps?) and boot off that, then run diagnostics to fix your hard disk without booting into windows.
$Extend$ObjId is an NTFS metafile - it won't ever show in explorer.
This article explains them: http://www.easeus.com/data-recovery-ebook/ntfs-file-system-metafiles.htm