downloads stop after a few seconds on my laptop

Fellow Linux n00b has the following question:

After installing Suse 11 on my Hp 6715s laptop, I found out that there was no real driver support for my Wlan-card (broadcom bcm4312), so what I did was installing ndiswrapper, mounting the windows driver, and I was easily able connect to my Siemens Gigaset Router, having full speed surfing in the internet.

However there is still a tiny little problem:

every and each download that I start breaks up after just a few seconds, going from normal driver- or videodownloads to linux repository updates (webpages, that arent too big work perfectly).

I use Knetworkmanager and it doesnt show that the connection breaks up.
Also, I have already tried to plug in a normal network cable with the the same laptop, into my router and the problem stays the same - so it cant be from the Wlan configuration.

I am somewhat desperate here, so could some kind soul please help me?