Help w/ firewalls?

Hi,

I was hoping someone could shed some light on firewalls for me.

I have a small home network. I have a dsl modem and a d-link router currently working.
I have been considering putting in a extra pc as a firewall (just for fun) and was curious how this is supposed to work.

The router is set up as the dhcp server so my network receives ip addresses from it. But if I install the firewall (i think this is correct?) it will be between the modem and the router. Do I set the firewall up as the dhcp serer then? If i do will itbe able to send IP addresses to pc attached to the router or should i assign static ones.

Thanks.