I do not quite understand what you want to do, so I suggest... correct me if I'm wrong...
you want PHP to give a variable the value of an textarea of a different HTML Page like $textvar = htmlfile.textarea.value; ???
That can't be accomplished, I suggest you know what server-side means... if you don't have a look at some PHP Tutorials and than you will understand why there is no other way than the one Lauri told you to get the value of a textarea in an PHP-Variable
Second suggestion, you want to parse a different HTML Page, taking some Values out... There are many ways to do that ... I use fopen
fopen("http://www.the_domain.com/the_file_you_want.html", "r") that is probably not the best solution, but it works fine for me and I only needed it once ...
Hope that helps
cya Rob