Internet stops working after 20 mins

[Martin Steen Nielsen <martin.steen.nielsen@mail.tele.dk>]

Greetings everyone
I posted this recently in debian-knoppix, but I guess this is a better place.

I've recently installed linux, using knx-hdinstall. Everything was correctly 
auto-detected. After a few days, I noticed something strange. Sometimes when
browsing, my internet stop working. A reboot would bring it back. Currently I 
have cron to run networking stop/start every 15 minutes, to keep it running 
in order to keep the line open for my download client. I don't think it's the 
the download client (lmule), eventhough it seams to appear more often, with 
lmule runnig in the background.

My netcard is a 3com 3c905b connected to a Linksys DSL router.
I ran dist-upgrade once, but it did'nt solve the problem. Could it be a kernel 
leak somewhere ? I'm using an unmodifed kernel 2.4.20 

Thanks
Martin