My First Linux Firewall Box From HDD Install

I've had a fantasy of setting up a Linux firewall computer to protect our Windows computers here, or failing that, at least setting up a Linux machine as my primary internet computer. Need plenty of advice if you can offer it, I don't really know much about Linux.

Built up a MODT (mobile [CPU] On Desktop) computer using a laptop hard drive, because I wanted to try making a low-energy computer for a change. Has no onboard CDROM or DVD, but have acquired a nice USB2 external that succeeded in booting Knoppix and performed a Knoppix HDD install, version 5.1. It's an all-in-one board and I've installed no cards and want to refrain from it.

After addressing a small issue with permissions discussed in the HDD install forum here, I managed to perform an apt-get update and upgrade, and got Knoppix to configure my network chip so I can now go online with the new box. So far good. BTW, using a Zyxel X-550 router.

First big question:
This Mobo has only one LAN connector. Do I need more than one network connector to properly use this box as a firewall? I don't want to add another PCI card if I can avoid it. (This question pretty much shows how much I know I'm sure.)

Other big question:
What should be my next steps? I'm a Linux novice really, and I've always run away from networking issues. Can anybody describe or direct me to some infos or resources for how to easily as possible achieve my goal, or what I need to look at? I'm really trying to keep it simple and avoid steep learning curves if I can. At least for now.

Thx for your attn., the minnow

I'm not expert on networking and I maybe wrong.

But for big question number one, I think you need another LAN card.

Here is what I think your setup should look like:

internet ==> 1st LAN card ==> Linux server with firewall/DHCP etc ==> 2nd LAN card ==> switch or hub ==> all other PCs

Again, I maybe wrong. If anyone has a better solution, please speak up.

If what I think is the only way, then you may want to go for your plan B. Just use the linux box for internet surfing.

Rgds,
Chip

Hey Chip, thanks for the reply. I may need to build up another computer if I need to put in another LAN card. It is possible with this home-made case but not really a good idea. (I built the case for a different project actually, and just wanted to put it to use.) Which I may have to do, but at any rate I'm just happy to have a Linux box again. Cheers, minnow