Firewall Implementation Strategy ?

[Vijay Kumar <vijay () calsoftinc com>]

Hello,

Currently we are havig a software firewall and the DMZ is in another Private Subnet. 
We use Port Forwarding from the software firewall to access the DMZ servers from outside. 

I have seen other implementations of Firewall where the DMZ is in a seperate subnet with Public IP Address. 
> From the Firewall we allow only access to certain ports. 

Can someone tell me the Pros and Cons of each of this implementation ? 

I need to know the different types of firewall implementation so that I can redesign the new implementation. 
Where can I get some good guidelines for the same ? 

Regards,
Vijay.