If you want it to integrate with the current UserCP, you'll need to add your php to the usercp.php file then add any templates that may be required to display your php information.
That being said... the profile page is different. The profile page is member.php so the same holds true however you'll need to edit the member.php page. You can pretty much do what you want with it if you're careful.
You'll have to register to see.. but
www.pixeladdiction.com has a very highly modified member.php file and several additional templates added just click a username.