Hey, welcome to the board.
I have alot of knowledge with HTML so PHP shouldn't be any trouble i think
hehe... php and html have absolutely nothing in common. one is a programming language, the other, markup.
Anyway, to the point. This sort of question is more specific to phpbb than to php itself. It might be best if you asked in a phpbb forum (this would be like me asking a linux question in a C forum), or atleast narrow down the relevent piece of code and let us take a look at it. If you can narrow it down you may even be able to fix it yourself. Html is resonsible for how the page looks, not php.
Myself, ive never even looked at phpbb's code.