Got a quick question. On http://www.sliderwall.com/ you can download a free sample which you can only use on your non-commercial website. I downloaded the code, and got it to work. I want to implement this on my commercial website. To use this, you actually have to pay $20,- dollars for a "license".

My question is: do I really have to take it serious? I modified the whole script, I only used a couple functions out of the whole plugin. Am I still forced to buy a license or can I just use the modified script onto my commercial website?