Slow web access over ethernet, but fine over WiFi.

Hi,

My XP desktop is ethernet connected to my 3com dsl router.
It starts off fantastic, but after a week or so, it becomes unbearably
slow.
I then give up, and go back to my humble USB ADSL modem for a few
days, and then, on returning to the router. it seems to be ok for a
week or so.

My aged laptop however, gets great response from the same router,
using the wi-fi link, all the time.

Any idea why this might be, and how I can resolve it for good?


Thanks.