ok so what do you mean he can't change the $ to £ - is he trying to calculate the price in pounds from US$ ? Or is it just a display problem?
Another important question - is he using his own software or is it a CMS or someone elses code that he has just put a design over the top. Looking at the webpage is useless. It might actually be better if I spoke to him, as he will know entirely what is going on.
Another thing that could be wrong off my head is that if the php is including another php file and the permissions are wrong on the other file then the code will not execute, but I really need more info. The php files might help but still need to know what is wanted.