How to find out DNS server IP used by my router
You can do one of two things:
If your router is just passing Comcast's DNS servers then you can issue an
ipconfig /allat the command line and it will tell you (Comcast's servers would be 68.xx.xx.xx not 192.168.xx.xx)If your router is passing itself as the DNS server, then you should be able to go on the router's admin interface status page and see what DNS servers it got from comcast's DHCP server.
I can't find the link right now but there are DNS-based domains which will accept a query and return the IP address of the requesting DNS server as the "resolved" answer. They won't report all your configured DNS servers but they could be useful when you don't have access to the DNS box.
A web-based page which include this info is http://www.dnsstuff.com/tools/aboutyou/