CentOS - Jun 2012 - Network Device control by Virtual host - Possibility & Security - Centos 6.2

Is it possible to pass the Network port to a virtual host and have a
minimal Firewall, IDS/IPS install there and this virtual host to be
the Gateway to the Network for the host as well as other virtual
hosts? I am talking specifically Centos 6.2 & KVM/Xen.

Also, what harware requirements need to be met.

And most of all what security implications. Normally minimal software
at the perimeter of the host should be a positive, but does
virtualization impose any weaknesses?

Rgds.
Sanjay.