Win XP and Scandskw/Defrag

Hello,

My computer was upgraded to Win XP professional. When I use Window Me, I can
clean my computer regularly by the use of scandskw, cleanmgr, defrag, etc.
But right now, when I type scandskw and defrag, I got error like " couldn't
find the file of "scandskw", "defrag", make sure the correct path or have
the libaries available.

Any help ?

Thanks
Heidi