How To Stop 1 User Logging On, On 2 Computers

Hello,

I have a domain, the domain controllers are Microsoft Windows Server 2003 Enterprise Edition. What i want to do is to stop careless users from login on one computer then leaving it logged on then walking off and login on another computer. Is there a way to stop this? Is there anything in group policy?

Thanks Alot

Zak
E-mail: zakflemingo@gmail.com