I'm using the CentOS 6.3 Live DVD x64 version; however, I can only access Google and IPs living on my LAN (haven't tested external IPs) in Firefox and Konqueror. Yum can't access mirrors as it claims sub-1kb/s speed and Xchat can't completely finish connecting to servers. I've tried this (trying to use the instruction given make NM unable to connect to the internet, regardless of DHCP with custom DNS or static, with or without custom MTU)
#centos was completely useless, they think it's a memory problem (yeah right... 1 GB isn't a lot, but it's not the problem)
My other specs: SiS 191 GBE networking, connecting over a DD-WRT wireless bridge on a WRT54G router connecting to an Actiontec R1000H router.