O man, you guys are making this too complicated. Trying to use the router is making this unnecessarily complicated. Your comcast modem/router is your current router and more than likely already has WiFi on it. Comcast usually uses a ridiculous name like CBCI-XXXX-2.4. That's your network.
But, like I mentioned earlier, all unnecessary since the Comcast has its own WiFi. If you haven't changed the admin password, you can go to
http://10.1.10.1. Username is usually cusadmin and pw is highspeed.
Direct link to WiFi config if Comcast Biz: (set the wifi PW here) For future reference, Bert is right about disabling DHCP to use the router as an access point. The first step is to set the router IP within range of your current range. E.g. 10.XXXXX, then disable DHCP. This turns the router into an access point.
The trick that gets most people is that you can't use the WAN/Modem port, you have to use one of the 4 switch ports to connect it to the other router.
There is of course another option which is to just buy a dedicated access point. As low as $20 and save the headache especially if you're just testing it. I would go with Ubiquiti if it's for production usage.
http://amzn.to/1MIuKOC
.png "ACUF Donor I")
