You might already have a shortcut that will do it for you. It would be on your desktop and say 'Set Explorer as my shell' or something similar. If you don't have that, you can do it the old-fashoned way.
Go to C:\WINDOWS\SYSTEM.INI and change

shell=C:\LITESTEP\LITESTEP.EXE

to

shell=C:\WINDOWS\EXPLORER.EXE

then restart, and it should load up explorer.
Keep in mind my file paths will be different than yours are. I don't know where things are on XP.