T-Mobile datacard freezes laptop

I finally got my datacard to work on my Fujitsu Siemens Amilo - up to point!
This is really a laptop problem, but I thought I'd ask here.

When I finally bit the bullet and re-built the laptop, at first things
seemed to go well. Comms were established, and Antivir was able to download
updates. However, when I launched a browser, after a few seconds the
machine locked up and the screen went dark. Power off was the only way out.
I eventually found some software on the T-Mobile download page (why does it
have to be hidden so obscurely on their site?) which was offered in case
you had lock-up problems. I installed it (though there was no obvious
installation method), but this made no difference. I then tried the
alternative software from Option, and it seemed to work after that.
However... I now find that it only works running as Administrator. Although
I can launch the Option software when logged in as 'Chris' I still get the
freezing syndrome. Logging back in as Admin, and it still works fine.

Ideas?

--
Chris