Finding lost files in Win NT

We have a machine running NT 4.0. The client wants me to recover some word & excel files that the computer “lost” when he loaded a newer version of outlook. I tried doing a *.xls & *.doc in find files, but they are not there, nor are they in the temp files. I am not that familiar with NT – does anyone know any way I might recover these files? Oh, and the client cannot remember exactly what the names of the files are.