Z- Visa renewal and temporary residence registration

I working in China with Z-visa since Dec 2010.
My Z-visa and Residence permit are from my Beijing Representative office.

I got temporary residence registration in Beijing (hotel) while getting residence permit in December 2010.

My projects are located near Shanghai, so I took an apartment in Shanghai and staying in Shanghai.

1. Do I need to do police registration with Shanghai police, as I changed my residence from Beijing Hotel to Shanghai Apartment?

2. If I register with the police for temporary residence registration, what are the tax related issues?

3. I want to renew the Z-visa in Dec 2011, can I use Shanghai residence temporary registration for Z-visa renewal?