I'm trying to set a little house network. So I've machine (server) with mandrake 9.1, I set up my internet connection to work normal ( Kppp). I have to set my DHCP server also.
I've configured 'sharing internet connection' (control center) and eth0 (DHCP,Gateway etc.), but
when I connect to internet with eth0 status up, my modem is connected, but I can't ping ip numbers... when I set eth0 status down and I redial I can ping ip and normaly work on internet...
Why??? Is it problem in dhcp.conf file or some other? I know that I'm soing something wrong but I don't know what. please help

Probably because you set the gateway to eth0. When the lan comes up it is switching to the default gateway. Remove the gateway and use ip maquerading.