Rob,
Hi. The postal code is not one of the default user tags that is available, but, no worries you will be able to get the current users postal code by creating a SQL token. SQL Tokens can use other tokens throughout the module, so you can use the $(USERID) within the SQL to gather the users postal code. Now I did a little research and setup this scenario on our test site so you should be able to get it working without much trouble.
The query would depend on your DNN installation, I tested on the latest DotNetNuke 4.4 release and I believe this should work for almost all 4.3.x releases...
Step 1: Within the settings create a new SQL token and name it PostalCode
Step 2: Use this as the query:
select PropertyValue from UserProfile Where PropertyDefinitionID = 30 AND UserID = $(USERID)
Note: The property DefinitionID of 30 is the definitionID for PostalCode. IF you are wanting to get other extended profile fields or just wanting to know what the definitionID for those fields is you can go to Host, SQL and execute this query:
select PropertyDefinitionID, PropertyName from ProfilePropertyDefinition
Step 3: After adding the PostalCode SQL Token, navigate to add content and add content that will include that token. Example: The user that is signed in has a postal code value of $(PostalCode).
That should do it...
-Chad