Driving me mad!

I am trying to use a vlookup (to another sheet) that has dates from 2005/6 -
I need to match corresponding dates from this year to previous years, i.e.
1/3/07 in sheet 1 needs to return the data next to the corresponding date in
the previous year's column(2).

Column D (sheet 2)
Dates

Column E (sheet 2)
Values

Column A Sheet 1
Dates

Column B sheet 1
Values

Column E sheet 1

Vlookup formula.

I have tried various permeatations of formula to no avail, such as
Vlooup(left(a3),left(mar06),2)

It doesn't seem to like the Left function. I've also tried the DAY function,
also to no avail.

Thanks for any pointers.

Martin