1. Dont worry I have checked on several broadband forum sites and many people have successfully set up Tiscali with the Netgear router I have suggested to you.
(However it is evident that Tiscali is almost as hated as an ISP as AOHell!! - but not much you can do about that now if you've already signed up...

)
2. The Netgear DG834G router I have recommended has an inbuilt modem to connect directly to your ADSL connection.
You state that Tiscali are ' likely to give you a USB modem' - does this mean you havent signed up with them yet? - if not go elsewhere..
If you are already with Tiscali, let them sent you their modem, then bin it and buy the Netgear router...