Hi Alan,
You cannot exceed 255 columns that is a specification limit.
For this and other specification limits see
HELP (or F1) --> Index (tab) --> specification
There are other spreadsheet packages that do handle more
columns, but they aren't Excel.
In Excel you would have to use two spreadsheets.
If you do not currently have more than 255 rows and never intend to
you can transpose the rows and columns. It probably won't look
very good as you most likely have your long descriptions in column
A of the rows, but it would provide a means of keeping your data
in a spreadsheet if you will never need to exceed 255 columns
once the data has been transposed. See TRANSPOSE in help.