InfoPath Dev

I have tried searching around and throughout this form but have found nothing. I am needing to run some rule (validation or action, not sure) that would check if a text box begins with a number that it is not valid then. Basically I have a text box that is allowed to be entered numbers and letters but I do not want it to start with a number. How can I do this. It could be really obvious and I am just not thinking correctly. Any help appreciated. Thank you.

Just use a formatting rule with a condition that matches a regular expression where that regular expression is one or more alphanumerics at the beginning followed by anything. The regular expression dialog shows you some samples and you can infer from them how to create the custom pattern or you could just read up on regular expressions via Wikipedia or whatever. Should be pretty simple.