bizarre network issue

[Tom Daly]

hoping someone will take this on, preferably straight to me so as not to 
bore list :-)

topology:
- in basement:
Surfboard cable (Eastlink if it matters) modem
   four ethernet ports, one of which feeds
Debian firewall/router box feeding hub on 2nd floor

- 2nd floor
hub feeding
Kubuntu box (mine)
XP box (wife)
Trendnet wireless router

- 1st floor (or wherever)
XP netbook

this has worked flawlessly for many years- recent new is modem.  Several 
days after it was here, I can't get out to internet/ TBird email on 
anything (cannot connect, try again says Firefox)

I can (as I am doing right now) ssh from Kubuntu to Debian, telnet to 
Chebucto mail, read/compose mail
so it feels like my network is working and Ye Internette is right there

from Debian I can ping google.ca by name or IP
I can't connect to google by name or IP on anything
so it doesn't feel like DNS issue to me

I can plug netbook directly into cable modem and get out fine

I can plug wireless router directly into cable modem, netbook into router, 
get nothing

I can unplug netbook from router, type in IP of router and get into admin 
pages, make and save changes, log out / log in and my changes are there- 
so wireless is working as well

Eastlink says from their end modem looks golden, and won't touch anything 
further

I've made no other changes to anything since known-good behaviour went 
south

anyone feeling adventurous?