Remove the $ from in front of the 3, as follows:

=IF(ISERROR(VLOOKUP($B3,rawdata,1)),"",(VLOOKUP($B 3,rawdata,1)))

then copy this down - you will have $B4, $B5, $B6 etc in the next few
cells. I assume "rawdata" is a named range in the other sheet.

Hope this helps.

Pete