LinuxQuestions.org - problems routing with single NIC

Hello guys:
I am running a Fedora Core 4 that I want to set up as a packet shaper (bandwidth shaper).

First of all, I want to configure it as a router, to have all the LAN traffic passing through the Fedora machine (configuring the Fedora machine as gateway for the other LAN computers)
but the problem is that this machine has only one (WIFI) network card.

1.- I have a DSL-router with an internal IP 172.16.0.200

My Fedora machine has:

wlan0 Link encap:Ethernet HWaddr 00:4F:62:00:B3:CE
inet addr:172.16.0.220 Bcast:172.16.0.255 Mask:255.255.255.0
inet6 addr: fe80::24f:62ff:fe00:b3ce/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:12662332 errors:0 dropped:0 overruns:0 frame:0
TX packets:12606640 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3668574360 (3.4 GiB) TX bytes:3690491544 (3.4 GiB)
Interrupt:11 Memory:d8020000-d8022000

wlan0:1 Link encap:Ethernet HWaddr 00:4F:62:00:B3:CE
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:11 Memory:d8020000-d8022000

What I want to do is configure the LAN computers in the 192.168.1.0/24 network and use 192.168.1.1 (the Fedora machine) as gateway.

I activated IP_FORWARDING but doesn't seem to work (what the *** am I doing wrong?).
I tried both the 'echo 1 > /proc/sys/net/ipv4/ip_forward' and the "net.inet.ip.forwarding=1" in the /etc/sysctl.conf file.

Any hints? After reading and trying so many things I am lost.

I tried firestarter but doesn't sees virtual devices (such as 'wlan0:1')

BTW: how can I try if routing works properly?
I mean, what tests could I do from the command line to see if routing is working. This is beacause usually I have no access to other computers in the LAN (where I could configure the gateway and check if it works).

For example, if I telnet my machine from Internet (my office), I have the router forwarding common ports to my Fedora, so I can access via ssh or vnc.
From there I do a telnet to itself using the LAN IP address (telnet 192.168.1.1) and I get in.

If I do 'ping www_yahoo_com' it resolves the IP and pings correctly.
If I do a traceroute to www_yahoo_com I get nothing...

I think this proves my setup is not working properly.

Any advices are welcome.