You didn't mention running DHCP in your first message. Run "/sbin/ifconfig" to see if the NIC has an IP address. The DHCP client on the eMachine should update the /etc/resolv.conf file with the gateway address. This is the file that contains the nameserver (DNS) addresses. It may look similar to this:
There may be a config option for the DHCP client where you indicate whether it can edit the hosts or resolve.conf file.
Enter "/sbin/route" to check if you have a default gateway:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
jesnet * 255.255.255.128 U 0 0 0 wlan0
link-local * 255.255.0.0 U 0 0 0 wlan0
loopback * 255.0.0.0 U 0 0 0 lo
default router 0.0.0.0 UG 0 0 0 wlan0
In place of the "router", should be the name of your internet connected computer (or IP address). One oddball thing to check, is to make sure you don't have one of the computers named "localhost". If the other computer tries to reach it, it will resolve to itself instead.
I've found in the past that I needed to modprobe the "ip_conntrack" module before IP forwarding would work. Also make sure that you have the ip_nat module loaded (lsmod | grep ip_)