buy an ethernet rooter with an inbuilt ADSL moden
USB modens dont work well with linux and if you get it working it will never work as well as it did in windows
you will need to make shoure that linuxs sees your ethernet card with is usually fine. The advantage with this is that you can wire up lots of computers and shear the net connection with as many computers as you like with no extra cost to you internet bill and tend to be more stabler than USB modems and the like. make shoure that your rooter has an in built ADSL modem
if you need dail up the a serial modem will do that job rember
that they are all hardware modems with an easy interface that is easy for linux and windows to command
the reasion for these silly USB modems and many if not all PCI cards is that they use computer programs to take a way electronic hardware that cost the consuma letting the computer doing some of the work and tend to be smaller to and cheeper [ some times they may say hardware moden PCI or USB, just egnore them ] often called
winmodems
here are such models UK web site.
http://www.ebuyer.com/customer/produ...ice&show=stock