parsing parsed pages?

I have been wondering for a while how I could parse a parsed page... I tried doing this in ASP and decided it would not be possible. (although i could be wrong, still somewhat of a newbie when it comes to serer side script) Why you may ask well the reason is i wish to filter a parsed page so that it could then be presented as a text only page and therefore would be useful for partial sighted people etc.... example at www.bbc.co.uk where they have a text only option which parses pages and presents a text only... if this can be done with php i'd be very happy, if not how could i do it? all i really want to do is load the contents of a html file into a string then i could do the rest however this becomes slightly more complicated when the pages are server parsed... anyone?