802.11b WiFi routers, on Comcast or similar fast connections, are a big no no.
See my blog post about it.
Turns out most of the 802.11b routers have only an 10 Mbps router port, where the 802.11g I tested (and have now) has an 100 Mbps router port.
Was killing me trying to figure out why I couldn't get the speed.