two linked files maintained by Sharepoint

Currently, I have one excel file which has both data entry and charting in
it,
Roughly about 3Mb file. I would to split this document into two pieces:
the data entry portion and the charting portion, where "chart.xls" would
reference the cells in tdataEntry.xls"

The data entry portion is too complex, to store just as a complex list in
Sharepoint.
But we don't need to have each use check in/check out the entire 3 MB each
time.

1. It is possible to have two linked Excel documents in Sharepoint? Thus,
a user
could to check out only the "dataEntry.xls" or both "dataentry.xls" and
"chart.xls"?
Can anyone point me to a good example of how to do this?

2. Or is it possible to use the Spreadsheet Web Parts and create dynamic
charts
based on the last checked copy of the Excel sheet? Thus, the charting would
be on
a sharepoint site, but I would only need the "dataEntry.xls"

Thanks in advance.
Tom