DMZing a UML VM

Hi,

I run a VM (A Debian stable UML installation) on my laptop.

My laptop is connected to the internet using its wired ethernet
interface, eth0.
My VM connects to the host machine using tap device tap0 on the host
machine.
I've enabled nat on the hostmachine which masquerades eth0 and have
also enabled ip forwarding.

I'm not security guru and I doubt if my laptop is secure from the
internet.
I'm using my VM for P2P application execution.

The only firewall rule I have for my laptop is:
iptables -A INPUT -i eth0 -m state --statue INVALID,NEW -j REJECT;

My desire is to keep my VM fully naked to the internet (In a DMZ) while
keeping my laptop secure.
I've tried finding documents on DMZ which explain the concepts and not
the commands but haven't found any.

Any help for the above mentioned problem is appreciated.

Thanks,
Ritesh