What is the equivelent of ISNA(vlookup) in Access 2003?

You'd probably want to use DLookup(), which will return a single value from a table or query and combine that with IIF(), which tests a condition and then returns an argument based on whether the condition was true or false.
However with that said, one place you don't want to use Dlookup() is inside a query.  What the DLookup does can be accomplished in a query just by using table joins.
IIF() has three arguments:

IIF(<condition>,<value to return if condition true>,<value to return if condition false>)
Dlookup also has three arguments:
Dlookup("<name of field to return>","<Name of table or query to look in>","<Where arguement to filter the data>")
  You can look in the on-line help for more specifics or bounce back here for more detail if you need it.
JimD.
 

What I need to do is compare my 2 queries if cust has a value in  field x tell me...

Do you mean iif ([query1].[customer], "yes", "no")  

Expr1:iif([Query]! [Customer #] , [Query (2)]![Customer #], Yes, No) tells me that the expression has an invalid .(dot) or ! operator or invalid parentheses  You may have entered an invalid identifier or typed parentheses following the Null constant

I have also tried this:
Expr1: IIf(DLookUp("[Query]![Customer #]","[Query (2)]![Customer #]", is not null, "Yes","No")
and it won't let me out of the criteria box.

I'm a bit confused where your using this; is it in a query?  If so then as I mentioned, you really don't want to be using Dlookup().
Let me know how your using this...
JimD.

I wouldl ike to know if a value in a certain field in my query exists in query (2)  I have tried what I interpreted you to mean both the iif and the dlookup and cannot get either to work.

Thank you for the concise information!