Creating a query where a field not in table needed

From: Mandorallin (Mandorallin_at_discussions.microsoft.com)
Date: 02/27/05 

Date: Sun, 27 Feb 2005 08:51:01 -0800

Opened the query in design view. I have created a new field, the value of
which is calculated from other fields. I have to use and "If"/"Iif"
statement. I want it to be "If value in field NOT equal to this value, do
this..."
I am having problems with the NOT bit. What do I type? And please be simple
with me :)