Excel 2007 : formatting cell so it doesn't convert to date

I have data previously entered into a spreadsheet that contains numeric values separated by a front slash. For example 01/99 or 23/23. Excel is trying to reformat that data as a date. I absolutely need the data to stay in xx/yyy format. To make things tricky there are also letters allowed, so I could have values like s/11.
If the value of the xx is less than or equal to 12, Excel thinks that it is a date and converts as such. If the xx value is equal or greater than 13, Excel leaves it as desired

The data has been exported from SQL Server 2005. Thanks in advance,

Try preformatting the column as text.

Or if you are importing to Excel have the file saved as .txt then when importing, a text to column wizard should pop up click delimited, click next, select comma, click Next and then select the column that is giving the problem from the main preview pane and select Text from the data column format area and click Finish.