Tom, it's usually installed as a part of windows.
Try looking under program files, outlook express.  Then you want a file 
called msimn.exe
Make a shortcut from this file to the desktop and name it outlook express. 
If it's not there, and you have the setup cd for that computer, you can 
install it from there.  If those two things fail, it's take your chances on 
the web time.
Let us know.