How to auto assign IP to Guest VM [KVM]?

Hi all,

Currently when I create a new VM, it obtains a private LAN IP and not able to connect to Internet unless I have to manually add my static IP then it's working fine.

Let's say I have 13 usable IPs, and I want one of them is auto assigned when I create new Windows 7 or Win Server 2008 VM on my dedicated server, how can I configure my network bridge to do so?

I'm running CentOS 6 64bit.

Thanks all