How do I replace a cable modem router with my own server as DHCP?

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http://askubuntu.com – My ISP gave me a really crappy router-modem-combination that lacks basic features. For instance you can't assign a constant ip to the mac adress of a client PC. I run a server for my home entertainment system and a storage server. Both should have a static ip within my LAN. So my thought was to disable the DHCP-Server on the crappy modem and let my home entertainment server do the ip assignments. I was thinking dnsmasq, but I don't seem to get it to work. I thought maybe someone can help me So the situation: is the server ip in LAN, lets say its mac is aa:aa:aa:aa:aa:aa and it i (HowTos)