Populate one field based on choice made in another

[perry kew]

I have a form called frmLibrary based on a table named
tblLibrary. Two fields in tblLibrary are FileLong and
FileShort

All the possible choices for FileLong and FileShort are in
another table called tblFiles.

Is it possible that when one types in an appopriate file
name in FileLong in frmLibrary that the FileShort field
will be automatically populated with the correct entry
from tblFiles?

Thank you.

--Perry