Comcast Business Modem and attaching other Routers behind it

Hi all,

I have an interesting situation that I need assistance to see if it was possible or if its not.  So I have a /29 block of static IPs that I am looking to seperate on the one Comcast modem.  I have the goals I am trying to acheive below

1.  I want to use 1 static IP out of the /29 for a primary network which I have working connected to an ASA.  I was able to succesfully achieve this using 1 port on the back of the modem.

2.  I want to use another static IP out of the /29 for a second router to have its own subnet.  I havent successfully been able to do this.  The model router I am using for it is a Linksys wrtg54. 

I hooked it up to the comcast modem on port 3(rj 45 connection)  on the back of the modem and chose the static ip option under my routers configuration web page and filled out my information but it will not ping or traceroute out anywhere.  Is this possible to do off of 1 comcast modem or do I need to configure something else that I am missing?

I have DHCP disabled on the comcast cable modem and bridge mode is disabled on it also.  If I need to supply more information I can get it.

Thanks