Windows Server 2003 – Group Policy Setup

Hi,
I was wondering if it is possible to use Group Policy to do the following in a Window (Small Business) Server 2003 enviroment:

1. prevent users from changing their desktop
2. prevent users from changing their screen saver
3. prevent users from changing their start menu

Additionally, is it possible to change a user’s desktop when they log into a machine on a domain? Ideally I’d like to lock down their rights then set up the domain so that the desktops automatically change to a standardised look and feel [same desktop, screen saver and start menu].

I should also note that there is a mixture of windows Vista and XP machines in the domain.

Thanks in advance,
chuck.