Rule integration for role validation

Hi,

I'm using the Rule module in conjonction with Regcode for giving some users a specific role.
I used the event "user has used a registration code" and i made an action which gives specific role. But without any condition for validating code, any typed string in the code registration field gives the role.
Here's my problem, it seems I need to add a condition for validating codes; I tried to use "check truth value", "numeric comparison", "textual comparison" conditions, but no results.
Could you explain how building the right Rule's condition for validating codes?

(Thanks for the port to D6)