Hit Alt+F2 and enter "gksudo nautilus" (obviously don't type the quotes) - this opens the file browser as root

Navigate to /var/ and right-click on the www directory. Choose Properties > Permissions.

Click the box next to 'Group' to bring up the list of users, and select the user you usually log in as.

Then change 'Folder Access' to 'Create and delete files'.

You should then have full access to the www directory from a regular file browser window as well as from applications such as your PHP editor.

Before I forget -- thanks str for the tutorial on setting up PHP! Just what I wanted - the facts and no fluff :)