Excel 2007 and saving as a web page
 

I recently upgraded to Office 2007. I have an excel document that I save as
a web page. Since I upgraded when I save my document it comes up and tells
me the document may contain features that are not compatible with the web
page. The only problem I seem to be having is that I have cells that have
0's in them that I want treated as letters so I have '00000 in the cell.
When I save the worksheet and then look at the cells they look fine, but when
I close the document and reopen it then all of those cells have 0 rather than
00000. This seemed to work before the upgrade - am I doing something wrong
or is this a potential bug?

Thank you,
Arica