What does exactly GPL license mean for my WordPress theme?

To put it like this:

I have created a WordPress theme for myself which consists of the following:

• PHP code – GPL v2 licensed like WordPress
• CSS files – All rights reserved
• JS files – All rights reserved
• image files required for the theme – All rights reserved

As far as I understand I can copyright all non PHP files in the theme, so my question is:

1. Does this licensing scheme (for file groups) violates the WordPress license?
2. Do I have to publish the PHP code of the theme so it is available to everyone?
3. If I were to make a WordPress powered website with my theme (with the same licenses as above) for someone else (who pays for the service), do I have to publish the PHP code of the theme so it is available to everyone, just the buyer, or anything else?

Does this licensing scheme (for file
groups) violates the WordPress
license?

No, only the PHP code needs to be GPL’d. A popular example is Thesis:
http://mashable.com/2010/07/22/thesis-relents/
http://markjaquith.wordpress.com/2010/07/17/why-wordpress-themes-are-derivative-of-wordpress/

Do I have to publish the PHP code of
the theme so it is available to
everyone?

You don’t have to publish it if your intention is to use the theme only for yourself. The GPL licence applies only when you distribute the theme to others.

do I have
to publish the PHP code of the theme
so it is available to everyone, just
the buyer, or anything else?

Just the buyer.