You will always have trouble proving yourself to a potential employer due to your lack of "commercial experience." My advice would be to think of a personal project or two and write some code. Not only will it give you something to demonstraite your abilities but it also allows you to practice your skills and even build on your confidence (if that is needed). If you can, make your project available online. Working demonstrations would be the best of course you would need somewhere that you can host CGI if you are writing a web based application. Otherwise somewhere like Sourceforge
is quite usefull. The interviewer might not be technical but if he/she has any sense they will ask one of their technical staff to look over your code and give their opinion. If you can collaborate on a project on sourceforge with some friends it would also demonstraite your ability to "work well with others."
Remember that amateurs built Noah's Ark. Professionals built the Titanic.