Hi D,
I don't know what you've read or tried, but I'd try turning off IPv6 first:
IPv6 troubleshooting http://support.apple.com/kb/TS3802
Open System Preferences > Network> select AirPort > click on Advanced > TCP/IP > Configure IPv6 >Off > OK > Apply > Turn AirPort Off > Turn AirPort On
Open System Preferences > Network> select Ethernet > click on Advanced > TCP/IP > Configure IPv6> Off > OK > Apply
http://docs.info.apple.com/article.html?path=Mac/10.6/en/11395.html
http://support.apple.com/kb/HT1714
And I don't know which browser/s you use, but since turned off IPv6 and gave Safari a good swift kick out the door, and use Firefox exclusively, I haven't had those annoying drops with the modem glaring red at me.