I am storing the name of closed invoice workbook files in a column of cells on another tracking workbook file. How do I reference those cells containing the filenames so that they display cell data from the respective files.

For example: In Workbook 1, say A1 includes 150.xls and 150.xls is the filename of another closed workbook. In Workbook 1 A2, I would like to display the contents of 150.xls A4. How can I refence Workbook1 A1 in Workbook 1 A2 so that it shows the contents of 150.xls A4. I want this to be dynamic so that all I have to do is type the filename and it diplays the contents automatically. Any help with this would be much appreciated. Thanks.