Im not an excel wiz but I know that say you have two xls documents and you want to make a reference in the second document to the first then you can open up both of them and then choose right click on the sheet in the first doc and choose move or copy and then choose make a copy and choose the second doc as the place to put the copy.
Now you should have a new sheet in your second document that have exactly the same data as in the sheet of your first document. Notice that on this new sheet, each cell refers to the first document's sheet so you can use those codee in the cells to refer to the first document.
You will need to experiment with updating, i'm not sure how it would work. You might have to reopen the document for it to update.

Hope this helps

Given two (or more) workbooks where A needs data from some other workbookB.cell,

in Workbook A at the location desired enter
=[pathtoWorkboolX.xls]sheetname!cellReference

Notice the sheetname!cellreference is how to get data from one sheet to another in the same workbook
so adding the [pathname] just addes the workbook location.

If you need to navigate on the directories, just start to enter =workbook and tab to get the file browser.
This will then create an absolute path the the file, eg
=c:\xxx\yyy\zzz\workbook

I am trying to create a second excel spreadsheet by copying the original. When I do so, I loose my formula in the new document. Is there a way to copy an excel spreadsheet without loosiing the formula?