The file sizes are not too large for Excel 2003 if they are ~25Mb. But
Excel 2003 only allows a total of 1GB of stuff open at one time, while Excel
2007 is supposed to allow 2GB.
I don't see how this affects your situation but I though you might be
interested.
I don't know is this is a help, but I have a problem with Excel 2003. I get
the unavailable resources message when I try to open a second 24MB workbook.
However, if I open a second copy of Excel and open the second workbook,
everything is fine. So I can open two copies of Excel, each with a 24MB
workbook, but I can't open one copy of Excel with two 24MB workbooks. Seems
to me that it has got to be an Excel memory management problem.