Replacing matched cell values

Hey guys/girls, i am in need of your help...again

i'll try to keep it short and sweet.

I have a spreadsheet with around 1000 rows on data.
in each row of data there is a number e.g. 2673 (all in their own cells) so in column A you would have a list of just numbers
in another workbook, the number thats in each row corresponds to another value e.g. 2673 = CE103. So this workbook has 2 columns. In column "A" you have the numbers(2673) and in column "B" you have what that number matches with (CE103)
i need a way of replacing all the numbers with what they equal
Workbook 1
A B C
2673 XXX XXX
513 XXX XXX
5107 XXX XXX
604 XXX XXX

Workbook 2
A B
2673 CE107
513 CDR57
5107 QV906
604 MNT57

There is an example of what i have (hope its understandable)
and what i need is, the data from workbook 2 put in to workbook 1. So instead of having 2673 in workbook1, i would have CE107. And the same for the others e.g 513 would be CDR57.
Hope someone understands what i'm trying to achieve here
Thanks in advance
Steve