Yes, you should be able to do this with a simple XSL statement. Assuming your schema looks like this:
Group
--LineItem (repeating)
----CreditCard
----Amount
Your calculated field will be this:
sum( LineItem/Amount[../CreditCard = "no"] )
To do this in the Designer,
1. double-click the field that you wish to calculate the total and click the Function button.
2. Click the Insert Function button, select sum, and then click OK
3. Double-click the link to insert a field, select Amount from the data source tree, and then click Filter Data
4. In the filter data, select CreditCard from the first drop-down, "is equal to", from the second drop-down, and then "no" from the third drop-down.
5. Click OK until you are back to the canvas, and then click Preview to try it out.
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge