One way would be to cycle through column A of table 2 and just do Edit|replace
with the values in column A and column B.

I put each table on its own sheet and ran this:

Option Explicit
Sub testme()

   Dim myCell As Range
   Dim RngToChange As Range
   Dim ValsToFixRng As Range
   
   With Worksheets("Sheet1")
       Set RngToChange = .Columns(1)
   End With
   
   With Worksheets("sheet2")
       Set ValsToFixRng = .Range("a1", .Cells(.Rows.Count, "A").End(xlUp))
   End With
   
   For Each myCell In ValsToFixRng.Cells
       RngToChange.Replace what:=myCell.Value, _
                           replacement:=myCell.Offset(0, 1).Value, _
                           lookat:=xlPart, searchorder:=xlByRows, _
                           MatchCase:=False
   Next myCell
       
End Sub

If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm