So you might have figured out you can limit the number of characters in a textbox in InfoPath, but what if you have to limit the number of words someone types? This came up in one project because they were posting the words onto a PowerPoint slide. To do this you must use 'data validation' (InfoPath 2007) or a 'validation' rule (InfoPath 2010) and you will need to select 'the expression...' for your first dropdown in the conditions and type this:
string-length(.) - string-length(translate(., " ","")) > 60 (or the number of words you want)
What this does is pretty straightforward - it counts the number of typed characters in your field (assuming you are placing this rule on the field in which people type - that's the string-length(.) part) and then it subtracts the same number of characters but with all the spaces removed (they were removed by the translate function) and this checks to see if the total is greater than 60...if it is, then your validation rule will tell the user something's wrong because they done typed more than 60 words o_O. This goes on the assumption that every space represents a word...which should be pretty close. Have fun!