Create a table from external data

Hi
Help please

I am trying to perform the function =IF(Test; ThenValue; OtherwiseDo Nothing).

i.e. by do nothing I mean to leave whatever value is in the cell, - leave it untouched.

Why ? (in case you ask)

I have 2 columns - a date column (A) & a value column (B)

I download some data from an external source which is a date & a value, say on 10/06/11 the value is 100
These go into "dummy cells", e.g. Y1 and Z1.

I want to make & keep a small table of DATE and VALUE so Cell A1 is tested for being 10/06/11 & if true, Cell B1 is filled with the number 100

The next day, new data is downloaded into Y1 and Z1 so the old downloaded data is overwritten by 11/06/11 & say 120.

In my "date column" I already have 11/06/11 & I want to put the new value, 120, into B2 and KEEP the previous value of 100 in B1

(The next day Y1 & Z1 will be overwritten with 12/06/11 & say 114 so I want to keep all the previous data & put 114 into B3)


Any help much appreciated.

Kind regards, Brian