You could record a macro when you do a file|saveas and modify it slightly.
I got this when I recorded one:
ActiveWorkbook.SaveAs Filename:="C:\My Documents\excel\book2.xls", _
FileFormat:=xlNormal, Password:="", WriteResPassword:="", _
ReadOnlyRecommended:=False, CreateBackup:=False
If I wanted to use Sheet1, A1 as the holder for the value:
ActiveWorkbook.SaveAs _
Filename:="C:\My Documents\excel\" _
& worksheets("sheet1").range("a1").value & ".xls", _
FileFormat:=xlNormal, Password:="", WriteResPassword:="", _
ReadOnlyRecommended:=False, CreateBackup:=False
I specified my folder and added ".xls" as the extension.
I'm not sure what automatic means.