default gateway not being assigned or kept

Hey all,this is my first time here so sorry if i do anything wrong or say something similarly.My problem is this;I have an unbuntu box with two network cards.  One of which has a netgear ADSL modem attached.  This connection successfully gets an IP address etc for the WAN connection.The second card is a on a class C home network, i.e. some reason a default route out to the first network card is not being set, if I set it usingroute add default gw where the IP address is the address of the external connection then I can get a connection just fine.However route then forgets this default gateway (quickly), I've looked in the syslog and found that the DHCP client is probably causing this to happen.If I connect the modem to a Windoze box it works just fine.My questions are these;1. Should ubuntu be setting the default gateway route by itself?  If so why do you think it isn't?2. In the Gnome configuration for network there is an option to set a specific interface as a gateway, when I set this, it seems to forget by the time I re-load the applet and doesn't solve the problem.  Is it possible to set this manually in a configuration file so that eth1 is the default gateway?3. How can I make this all work the way it should?Thanks,Twiggy