You'll probably need to instead use a rule on the Expiration Date field. So in InfoPath Designer, on the Expiration date, you'd add two rules. One have the condition that if the date is less than today (use a formula, then use the today function) set the field that needs the value to Expire. The other rule, also on the expired field, would be if the date is greater than or equal to today, set the field to Current. HOWEVER - that would only run when the expiration date changes.... So - I'm wondering if what you really need here is SharePoint workflow?
Hilary Stoupa
