|Ok, this is getting a bit weird.|
If Workbook A and Workbook B are in separate directories,
then you need to supply the complete path name in Workbook B IE:
='C:\Documents and Settings\Owner\My Documents\[BookA.xls]Sheet1'!$A$1
After entering data into Workbook A, saving and closing Workbook A
if you then navigate to Workbook B, open it, it will ask you if you wish to update.
Answering yes updates Workbook B to reflect the changes in Workbook A.
Now here is the strange part,
If you have Workbook A closed and open Workbook B, the formula will display as shown above with the complete path, but if you now open Workbook A, while also having Workbook B open, then the formula reverts to the
If you then close Workbook A the formula reverts back to the complete path.
So it will work, but boy is it flakey.