Missing files

I need a lil help I have a few missing files on my comp and I am not sure how to get them back. To tell ya the trueth I am not even sure how they went missing. Anyways I need to know how to know how to get the following files back please something that is free would be great.
MSSTDFMT.DLL
MSMSGR123.EXE
there is also some sah or sar file missing I am not sure of the proper name I hope someone out there will now what I am talking about and help me find these files again. Thank You