At the risk of suggesting an overly simple idea -- in contrast to Al's which
can allow you to build a live, one- or two-way link from Visio to Excel --
you can also hyperlink the Visio shape to a spreadsheet. In fact, you can
link to a specific cell so when the user follows the hyperlink, the
spreadsheet opens with the target cell highlighted.
Note that this doesn't link at the data level; all you're doing is allowing
the user to navigate from the drawing to a specific location in the
spreadsheet.
If this idea sounds useful, look at the Visio help text:
For Visio 2002: Open the Hyperlinks and Web Pages chapter, then open the Web
Pages subchapter.
For Visio 2003: Click on Table of Contents, open the Visio and the Web
chapter, then open the subchapter titled Publishing to the Web.
To link directly to a cell, assign a name to the cell, then use the
Subaddress field in the Visio hyperlink dialog.