The easiest way to do this is to record a macro do open (I am assuming you are opening up the same document everytime).
1. TOOLS->MACRO->RECORD MACRO. Give the macro a name.
2. INSET->OBJECT->CREATE FROM FILE->BROWSE. Select the file and click on INSERT then OK
3. Stop the recording.
Thats it. Everytime you run the macro, it will insert the same file.
The other option (rather than inserting the file everytime), if all you want to do is update the content is follow step 2 above (ignore step 1). Then, before you click on OK, check the check box LINK TO FILE.
Now, everytime you make a change to the document you have just inserted, the content in the Excel file will also change. Automatically.