Comparing two columns in Excel-07 for exact match values in front of values in left column ?

Hi, I want to check for match exact values in column B with relation to column A. I mean I have huge data in both columns. Suppose that A has Invoice Nos & B has Invoice Values. Invoice Nos in "A" can be repeat for multiple times throughout "A". But Invoice Value for particular Invoice No should be same in "B". I mean each Invoice No. must hold same Invoice Value. But its huge data & there are thousands of Invoices & lines. How this can be done without any doubt of accuracy ?

Thanks in advance!