Windows defrag not replaced

Hi all.

I slipstream my own XP install discs & as part of this process I remove the Windows defragger & use Defraggler instead. My problem is that without the default defrag installed Defraggler won't replace it on the tools tab on the drives properties. It just comes up saying 'No defragmentation tool is installed'.

Is there any way around this or will it only replace it if it's installed in the first place?

Cheers