If what you are saying is correct, then you have some unusual-looking filenames on your site, which may be your problem.
On a login session on your web server, go to your web root directory. There should be a directory there called admin. cd into that directory and look at page.php. Is that a file or a directory?
If it's a file, then it would appear that your system has been set up to use some apache rewriting. Rewriting allows you to take a url that might look something like
http://example.com/news.php?month=04&day=03&title=hi+mom&kitchen-sink=true
and rewrite it as
http://example.com/news/04/03/hi+mom/true
If this is what's going on, you need to look at two things. First you need to find your rewrite rules which are either in the admin directory or webroot, or possibly in your apache config file. The rewrite rules will tell you what variables apache will pass your values of "modify" and "submit" into.
Then you need to look at your page.php script and see what it will do with the values you've just passed in.
The example above was shamelessly nicked from the excellent introduction at
http://www.zimbio.com/portal/PHP/blog/12
That site also has an example of achieving the same result in pure PHP - at
http://www.zimbio.com/portal/PHP/blog/13
there are probably local articles on the same subject here ob phpbuilder.com too!
