Right now you can get a broadband router that does NAT on your home network, and depending on the model, can do port filtering as well. They are not rules-based firewalls like the more sophisticated hardware/software combos, but they are fairly effective.
LinkSys has one for less than $100. (I have one)
Also NetGear, 3Com, and SMC all have models. Each includes a DHCP server to provide addresses to your local network and some even include a print server. For less than a hundred bucks you get NAT addresses, and all your local systems can use the Internet on your broadband gateway, whether it\'s DSL, Cable Modem or other.
Have fun.
-- R