Hows this?

The vlookup uses the 2nd sheet as a source table. Syntax of vlookup is as follows:

=VLOOKUP(A2,LookupTable!$A$2:$B$256,2,FALSE)

1st: Item to look up
2nd: Location of lookup table (note the $ syntax to stop the table moving if you move or drag the result cell)
3rd: Which coloum to return from the lookup table
4th: Allow loose matching...

Hope that helps..

EDIT: fixed a typo (not -> note)