Question : referencing 2 excel workbooks

Hi,

I have 2 workbooks in excel, there is one sheet in each both containing info about transactions.

basically I want to find out if the transaction in one, exists in the other.

So I have:
Woorkbook1, Sheet 1,
Date, Reference, amount
1/1/10, 123456, £100

Workbook2, Sheet 1
Reference, StoreCode, Salesman code,
123456,      123,             987

I would like an extra cell in workbook 2 just to say exists?

The purpose in this example is to make sure salesmen arent making up transactions (however this isnt the reason we are wanting the formula - it was the only example I could think of barring our own)

Answer : referencing 2 excel workbooks

Something like:

=if(ISNA(MATCH(A2,[Workbook1.xls]Sheet1!B:B,0)),"Does not exist","Exists")