I forgot regedit sequence

Question

when i starts my system after displaying WELCOME message in windows Xp , i see a dialouge appearing EXPLORER.EXE(unable to locate the componets) below i see BROWSEU.DLL is missing please reinstall the file

when i get in registry/...../shell / i can see the explorer.exe is there i dont know why this is happening. please help me how to reinstall this files beacouse i have imporatant data in mydocuments i dont want to loose that one. i need assistance wth step by step guidance.
thanks