Hi there I hope someone could help me

I've got a column of dates in column A and the sales for each date in column B

What I need to do is that I have to classify these daily sales figures into
weekly sales figures downloaded onto my "Sales!" sheet
Then I've created a new sheet "Sheet1!"and put the to and from date in
column A and B and the week number in column C

For example
Date From Date To: Week Number:
01/01/2006 07/01/2006 1
08/01/2006 15/01/2006 2

I would like to do a lookup in my downloaded daily sales figures and I've
put a formula:

If(Sales!A1<Sheet1!B2,if(Sales!A1Sheet!A1,vlookup (Sales
A1,Sheet!A:C,3,0),"Checking")

However it doesnt work, can somebody please help me and tell me what have I
done wrong and how should I put it right please?

Thanks a lot

Vivi