Hiya !
Very glad A&A were so helpful even for a non-customer ! LOL
They are a good bunch. You want your ISP to basically provide you with a perfect connection and then never talk to them again.
Tiscali will be nothing (probably) but grief and admin c*ck ups and when you do need tech support they will think you are just being dumb.
Anyways - to the modem in question...
Install sounds nice.
Sysem Prefs / Network / Ethernet (2 ?)
Click the PPPoE tab (even if Tiscali is PPPoA)....
Click the check box at the top 'Connect Using PPPoE' - this will enable all those pale greyed out options.
You will need Account Name and Password. I think this is the same as your login name and pass, but it may not be. Try your login and pass you have been given.
Tick 'Show PPPoE status in menu bar' for now as you may get some useful messages in the menu bar showing you wtf is going on...
When you've done all that, could you confirm if you are joyous or if you are still sobbing ?
(I think you've done all this already anyway...)
You may then need to go to the TCP/IP tab and do stuff there, but tbh I am not sure exactly what.
I'd guess it was 'Configure ipv4' - DHCP - and leave it to Tiscali's access servers to throw you a correct IP address, but I don't know how they work...
Give it one more bash tonight, but then, for sanity's sake, and to move to a more helpful ISP, I'd go with A&A or perhaps Zen that has been suggested. A&A's router, if you buy it from them will be probably 30 - 50 quid, and have your ADSL setup info already programmed into it by a nice geek. If you plug it in, I estimate you will be on the Net in 22 seconds.
Honest.
PS - Yes, iTunes and IPhoto totally rock. They are SO deliciously easy to use and stable.
Enjoy. Hope your IP connection gets sorted soon.