aol bt adsl modem software s

Hi, I'm from the UK. I am, well was using AOL ADSL broaband using a BT Voyager 105 ADSL modem. After installing Vista as a clean installation, my system no longer allows me to install the modem or the AOL 9 software properly. I tried several different ways and managed to somehow install the driver for the modem and did install the AOL software, but when ever I want to run the AOL software, I get an error which says that it has install a few more files and has to restart the whole PC!
The error just doesn't want to go away. I tried installing and reinstalling several times, with no success what so ever! Can someone please give me suggestions as to what I should be doing.
Also, to Microsoft, or anyone who can help me, I noticed that I have to activate my Vista installation within 15 days through the internet! But if I can not get my modem to work beofre that, what will happen to my system after 15 days? Will I still be able to maybe install XP again?
Thanks for reading. Hope you can help