After nearly pulling my hair out several times in the past couple days, Chris finally figured out what the problem with my setup was.
It turns out the Netgear router was talking to the router with PPPoE-framed packets, and the Netgear device itself was sending out Ethernet-framed packets, and only my Lindows box was choking on it. Windows, it seems, self-adjusted the MTU size.
This, after using tcpdump, ethereal, iptables -L, checking hosts.deny, hosts.allow, etc. At least I've learned a ton.