How do i code a VBA to ask the user to select which file to use

Try this

dim FName as variant

chdir "\\Via.novonet\dfs\LIFE\F\INVReporting\CONFIDENTIAL\Inv_Reporting_2012\Source Files\"
FName = Application.GetOpenFilename(FileFilter:="All files (*.*), *.*", Title:="Please open the file")
If FName = "False" Then
    MsgBox "You have not selected a file."
    Exit Sub
Else
    Workbooks.Open Filename:=FName
    FName = ActiveWorkbook.Name
End If
With workbooks(Fname)
        .Worksheets("Data").UsedRange.Copy ThisWorkbook.Worksheets("S29 Data").Range("A1")
        .Close False
End With