In Excel 2007, you can this with the built in "Remove Duplicates" feature.
In Excel 2003, you will have to make use of a spare column.
1. Suppose the data is arranged in range D250;
2. In cell E2, enter =if(countif(D250,D2)>1,"A",1) and copy down till E50
3. Now highlight E2:E50 and hit F5. Click on Special
4. Now under the Formulas radio button, uncheck all boxes except "Text"
5. Now Edit > Row > delete