Poor Vodafone USB modem signal

Last weekend I had to resort to getting a Vodafone USB Sim card modem for my desktop because Italia Telecom are too damn lazy to install a landline to my house.

Anyway, I am getting very poor reception and download/upload speeds and was wondering if there was a way of improving matters.

I have put the Sim card in my cell phone to find the best spot and that is by the window in an upstairs bedroom, which is totally impractical. At the moment I have had to wheel the computer to the opposite side of the living room to get at least some reception.

Is there some sort of box or antenna I can mount outside on the roof or some sort of Heath Robinson contraption I can build to improve preformance?

One other problem is that the USB cable that came with it is only about 50cm but when I plug it into my 1.75m cable it does not work even though the cable is fine. So not very flexible.

Thanks.