I've got kubuntu 8.10 running and I use verizon dhcp card for internet access. I also have a wireless home network. I am using knetwork manager and I cannot use two interfaces at the same time. I have to go to knetwork manager and disable the wireless (eth1) in order for the dhcp card to work. I have gone to the routing table and all routes are present, i've added ppp0 (dhcp card) as default, but I still have the same problem.

Have you tried disable NetworkManager? This once happened to me when I try to connect my WM6 as dial-up modem (rndis0)and my wlan0 died.

What would I use to manage the connections if not knetwork manager?

Well, if you cannot connect to network manually and you need networkmanager to manage your connection either wired or wireless, then disabling one of devices is the best practice. Somebody please correct me if I am wrong. Anyway you have alternative like wicd.

Are you using DHCP on your wireless card as well? If so, you might want to check your /etc/resolv.conf file. If your wireless card is obtaining an IP address after your external interface, resolv.conf is likely being overwritten with nameserver information from your wireless network. This would prevent you from being able to do DNS lookups to the internet.

no problem with that. The issue is that I need to disable one in order to use the other. So for instance if I'm on the internet , using the verizon dhcp card I cannot go out on my local network using the wlan (eth1) to get a file etc. I need to disable the verizon dhcp then enable the wlan to get on the local network. After I'm done on the local network I need to disable the wlan connection and enable the verizon dhcp then go to the routing table and add ppp0 (the verizon card) as a default route in order to get back on the internet. So you can see it just a bit of a hassle.

i would use w package like firestarter
http://www.fs-security.com/
and set the verizon card as the external interface (ppp0) as the external interface and the internal interface (eth1) as the internal interface, i used this to share a dialup modem connection with a lan (until i got dsl)
this could also be done direclty with iptables, but would require you to know how to use iptables

What does your routing table look like when you have both interfaces enabled?

What happens if you try to ping a computer on your internal network in this situation?

thank you frieza, firestarter did the trick. Now I can go on to the next challenge and share the internet connection on the local net.