Use a conditional value list. (Search the Knowledgebase for details on this.)
Or use a calculation field as the value source for your list of usernames.
If ( status = "Active" ; UserName ; "" )
The most confusing part to me is not being able to write a query stating "query XXXX WHERE XXXX == XXXX" I need a WHERE statement. LOL
That's what the IF function does in the calculation and that's what's accomplished with the conditional value list if you set up the relationship correctly, should you choose that route. (A conditional value list can be a bit more flexible here, but it takes more effort to set up.)
If you use the calculation field, you'll get exactly what you describe as the caculation field leaves out usernames that aren't "Active".
All setup and works nicely, read the sections in knowledge base too thanks again Phil! :)