Advice on bridge or 2 Ethernet card setup

[turnbui]

I am thinking of using a firewall in my new Mandrake 10.1 system. However my scenario has a slight deviation to the normal configuratiuon. I have perused FAQ's and other documentation and can find info on a bridge but again my needs are slightly different in as much as hopefully I THINK I know what a bridge is for though clouded understanding. When I have XP booted instead of Linux in my main machine I create a bridge between the 2 ethernet cards, set the other machine to use DHCP and everything works fine. I can share files with all the other computers and browse the internet. However, I want to learn about this fascinating world of networking and want to set my system up differently. viz:- I share an internet router with 3 housemates and have been assigned 1 port of their DHCP D-Link D504T router that uses subnet 192.168.1.0/24. This will be to my Linux machine on eth1. I also have a requirement to hang my own mini network off eth0 in my Linux computer. I would like to have my mini network on a separate subnet say 192.168.3.0/24. Is this possible and have access to the Internet as well as two way communications between the 2 local subnets? Am I setting myself up for a big headache? Any info would be greatly appreciated - I feel like I'm drowning in all the info I've read lately.