This is just an example. This little macro will SaveAs to the contents of A1.
Put c:\whatever.xls in cell A1 and run the macro.
Sub savetocell()
Dim s As String
s = Cells(1, 1)
ActiveWorkbook.SaveAs Filename:= _
s, FileFormat:= _
xlNormal, Password:="", WriteResPassword:="",
ReadOnlyRecommended:=False _
, CreateBackup:=False
End Sub