Changing a Text String into a Worksheet!Cell Reference

Basically I'm attempting to concatenate a couple of variables into a cell reference.

For instance

Cell A1- October

Cell A2- =A1&"01"&"!D4" which equals October01!D4 as a text string

Is there a function that would change the text string value of A2 into an actual reference to October01!D4 ??? I do realize that it would be easier just to actually reference A2 to =October01!D4 but I have many cells that have to reference a previous worksheet. When I copy One worksheet, I just want to Change field A1 and have all the references change to another worksheet automatically.

Hopefully I made some sense.

Thanks in Advance

Shaun