How to Copy *.dll File

If your System is Windows XP ,and it's File currepted somehow,then most of the time you setup XP , if your  *.dll file currepted then you can try very simply,turn on your computer normally if that could not possible then try to start save mood by pressing F8
Insert the bootable XP disk into your CD/DVD ROM, and go to RUN option from start menu and type  sfc/scannow and press enter.
I hope you will get rid of your problem.