I would use a nested for loop to scroll through your information. Although this can be time consuming, so if you have loads of data it would be better to use Access or SQL

For I = 1 to 1
firstname = workbooks("File1").worksheets("sheet1").range("A" & I).Valu
Lastname = workbooks("File1").worksheets("sheet1").range("A" & I).Valu
ID2003 = workbooks("File1").worksheets("sheet1").range("A" & I).Valu
For I2 = 1 to 1
if firstname = workbooks("File2").worksheets("sheet1").range("A" & I2).Value the
if lastname = workbooks("File2").worksheets("sheet1").range("A" & I2).Value the
workbooks("File2").worksheets("sheet1").range("A" & I2).Value = ID200
exit fo
end i
end i
next I
next

This code will need to be modified slightly: the column number, workbook names, worksheet names and the from and to values of the for loops. Change the from value to the same as the first row of data that is NOT the header. The to value should be the last line that contains data. If the to value will change from time to time simply set it to 19999 and add the bellow code into each loop (change any appropriate values

If workbooks("File1").worksheets("sheet1").range("A" & I).Value = "" the
exit fo
end i

Hope I have helped

regard

Russel