InfoPath Dev

I am a newbie to Infopath and am using the following set-up:  Infopath 2007 and WSS 3.0

I have the following lists in WSS:

 1) Location master - includes a unique identifier for each location

 2) Survey Responses - includes the location ID from Location Master, question number, and responses 

On my Infopath form I would like to autopopulate a text box with the location's response.  I can easily autopopulate based on one criteria but am struggling to do so with more than one criteria.  For example, right now I have a drop down for the location ID which will autopopulate the location name based on the Location Master list.  I need to set the text box based on Location ID and Question Number.  Any suggestions?  Can I use a filter?  What about concating two fields to make a unique ID? 

Any help is much appreciated - let me know if the question does not make sense and I will try to re-word.

Ok- so I was able to get my desired results by using a repeating table that pulls all results onto the form.  However I used the conditional formatting tool to only show those rows that are applicable based on the location ID and Question ID selected on the form. 

This works fine for now, but there could be as many as 4-5,000 records.  Does anyone see any performance issues with this many records?  Also, does anyone have better suggestions?