Intermittant internet connection on Verizon DSL thru RT311

We've got an odd one here.. There's 20 odd Windows 2000 machines on a 10/100 network.  Internet service comes in over DSL into a Netgear RT311, from there to a netgear switch, and out to the machines.  There are some other machines in a nearby office, connected by a wireless bridge.  

At any given moment, there is one machine on this network that has "the bug" ie:  at seemingly random intervals, it looses it's connection to the internet, while retaining intranet connectivity (shared drives, printers, etc)  This is evidinced by IM clients loosing uplink and then like minutes later logging back in, and interrupted web navigation +m page loads.
This symptom has jumped from machine to machine, it's on machine #3 as we speak.  

Possibly useful additional info:
All machines are served DHCP from the RT311, it has been restarted and resetup from scratch.
FTP, e-mail connections also do not work during these intermittant outtages.
The RT311 router is configured to send out a dynamic ip range from 192.168.0.20 up to .85, as there are some servers (print, file, DBS) with static IP's below that.
The machine that is experiencing the bug, appears normal ie: shows complete info via Ipconfig as having a DNS connection etc.  
Doing a release/renew seems to help, but the outtages only last about a minute or so, so it could just be "the bug" unfuckerating itself.
Any thoughts? Questions? Avenues of investigation?
Thanks in advance.