wireless networking - Netbook (Samsung N220) on Ubuntu 10.04 slows down WiFi for other computers

I encountered a really odd problem with my new netbook.

I am running Ubuntu 10.04 on a Samsung N220 Mito. So far everything worked fine.

Now I tried the machine for the first time in our work group where we have a wifi (with internet access) for all laptops. The wifi is controlled by a computer running Suse 9.3 which provides a DHCP server and imposes a firewall.

At the moment there is only a macbook in the wifi, where no problems with the internet or wifi connection are encountered.

Now coming to my actual problem: In addition to the macbook i connect the Samsung N220 to the Wifi.

1. Problem:
   My download speed is for some reason limited to 70KB/s max. This is neither a limitation of the server/website i browse on, nor a configuration of the netbook: at home i have > 500KB/s download speeds. Furthermore, it is not a default limitation for "untrusted" or "new machines" in the wifi, as for instance other new laptops get full speed internet with our wifi.




2. Problem:
   Once the Samsung N220 is generating traffic in the wifi, the wifi is slowed down dramatically for all other machines: I run a ping to the router from the macbook. The ping times with the N220 ideling are 2-6ms. When I start downloading or browsing in the web with the N220 the ping speed drops to > 800ms. Vice versa, when the macbook is generating the traffic the ping of the N220 to the rooter stays constant at around 2-6ms. So clearly, it is some problem originating from my netbook or maybe its treatment in the wifi.

Thanks for any help