alcatel shp + aMule = bandwith saturation

Hello,

I am writing here because I got a terrible problem I cant solve.

I have two workstations:
1 - slackware linux
2 - win XP

These workstations are linked with the Alcatel SpeedTouch Pro router.

When I active aMule on linux workstation the other one (XP) is not able
to surf the net, connections are very slow, even from the linux station.

I have a 6Mbit ADSL, I setted bandwidth in aMule to a minimun, both for
upload and download.

Even when aMule is not downloading nothing I got that problem. (with
upload consuming less then 6K!)

Note that I have natted two ports, TCP and UDP, requested by aMule client.

I hadn't this problem when I had a modem, so I guess the router is the
problem

Any ideas how to solve this situation?

thank you all!
Alberto