Don't buy any ad-ons for Excel - it can do all sorts of amazing things...
I think all version of excel have 'vlookup'
=vlookup(cell to look up,array to look in, column from array to return, false)
If the 2 tables match e.g. each are 100 rows long with unique value in a column, then all you need to do is sort the tables by the columns and then the value will line up... (ok sounds obvious but so many people miss this)
If they are NOT the same, you can use 'countif' to find which rows from table A are in table B, and vice-versa, then you will be able to remove any excess until they are both matching, then you can use the 'sort by same column' approach above...
It's worth trying it this way because computers sort a lot more quickly than they vlookup, and the vlookup only returns one cell at a time..
Hope this made sense?
I use excel way to much at work... one of the reasons I'd rather get a CPL!