All include does is load a file into the physical place where you put the command. You could just as well copy and paste the code in there. So anything available in the scope of the main page is available in the include code.
And what you include is a file not a URL... meaning that variables passed with ? will not be passed to the script. They are just a part of the file name string. What you need to do is split the variable in filename and arguments before loading the include.
Pathinfo() might help you, but I think doing a custom function for the purpose might be necessary.
In order to get the string og ?arg=1¶m=2 converted to variables, your will probably need to turn to variable variables (check http://www.phpbuilder.com/columns/robert20000928.php3)
Hope this helps
Martin