[Xenon]

first of all you have to require global.php in your bigroom.php

then make all your coding aso in your bigroom.php andd then use

eval("dooutput(\"".gettemplate('bigroom')."\");");

in your bigroom-template you can use all variables you have defined in your bigroom.php

oh, and of course a tip for you in general:
if you're new in coding php, you shouldn't start making greater projects at first...
try to get a feeling on all that things by just adding a few hacks and try to understand how vb sites work.
That's how i learned php-coding..