I made a couple more additions and I set it up so that it would degrade gracefully if the version of POI isn't high enough to support the features.
I also made a change to the way values are set in cells. Before a row was created every time a cell value was set. With newer versions of POI if a cell already existed in a row, it was wiped out when another cell in the same row was set. The new method first checks to see if the row exists and uses that. If the row doesn't exist then it creates it.
The ability to put JPEG and PNG images into workbooks was added. This works with the POI included with CF9. If someone tries to use it that doesn't have a new enough version, it takes the cell where the image was to reside and places a message that the POI version doesn't support it.
You can now stream the workbook directly to the browser instead of having to create a file first by using one of the new functions.

1. Added options for XLSX (Office 2007) files if the POI is the right version.
2. Added getRow function. This function will get a row or create it if it doesn't already exist.
3. Added getCell function. This function will get a cell or create it if it doesn't already exist.
4. Changed multiple functions to use getRow and getCell functions.
5. Added AddImage function to place an image in the spreadsheet.
6. Added AddJPGImage function to put a JPEG image in the spreadsheet.
7. Added AddPNGImage function to put a PNG image in the spreadsheet.
8. Added createBookVar to allow for streaming workbook to the browser without creating a file.
9. Updated create region to allow creation of regions in xlsx workbooks.