Cisco Firewall :: Configure ASA 5505 With TimeWarner Business Class Service

I'm trying to support a friend. They just switched to TWC Business Class from Megapath. They have a Cisco 5505 ASA and are trying to configure it to work with the new TimeWarner cable modem. But we can't get PCs behind the firewall out to the Internet.
 
We think it should be a pretty simple config. They have the ASA connected directly to the modem. The modem is running DHCP, and we''ve configured the ASA to get its address via DHCP. We have a Windows server behind the firewall; it can't get out the Internet either. It's set up to be a DHCP server and is giving IP addresses to the PCs on the network.
 
Laptops connected via wifi to a wireless router attached to the modem are able to connect to the internet, thus we know the modem is up and running fine.
 
Here's our running config:
 
ASA Version 8.4(1)!hostname ciscoasadomain-name opanslab.comenable password yYME2neTGgA0S1./ encryptedpasswd yYME2neTGgA0S1./ encryptednames!interface Vlan1nameif insidesecurity-level 100ip address

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