Thanks, Earl Kiosterud~ I got the partial of what I want already~
But the way you teach me, it still allow 'A2' to input as "KELVIN"...
And, I'll not only need a specify cell like 'A1' but anywhere as long as I
input "KELVIN" in anywhere cell. Then I can't input it again in any other
cell...
(Sorry, my English not very well. Hope you understand what I want :P)

"Earl Kiosterud" wrote:

Kelvin,

You've asked for VBA, but here's a way without it:

1) Select all the cells of the worksheet except A1. To do this, click A2,
then press Ctrl-Shift-DownArrow. Add column B to the selection by
Ctrl-clicking the column B header, then press Ctrl-Shift-RightArrow. All the
cells except A1 should not be selected, and B1 is the active (white) cell of
the selection.

2) Data - Validation. Set the Allow box to Custom. Enter the following
formula:
=B1<$A$1
Click OK.
--
Earl Kiosterud
www.smokeylake.com

"Kelvin Lee" wrote in message
...
Let say in 'A1' I input as "KELVIN", then this word will not allow anymore
in
anywhere in the same sheet.
How to do it?
What's the coding in VBA of it?