You have two columns of data. They can be on different sheets for all I care. You want to identify the duplicate information -- datum on one column that is also in the second column.
This example gives the assumption that column A has one column of data, and the other listing of data has the named area of "List". (To create named area, highlight info, Insert, Name, Define). Using column B, enter the following equation: =VLOOKUP(A1,list,1,FALSE)
If there is a match, you will see the matching information. If there is no match, you will see the "#N/A" error.