The security in Vista is a pain in the butt, however it is easy to get around. Run the setup.exe file on disc in Administrator Mode.
1)Go to My Computer
2)Right-click on the CD drive, choose 'explore' or 'view files'
3)Sort by File type and look for the relevant Application or .exe called 'install', 'setup' or something of that nature
4) Right click on that file, Click on "Run as Administrator"
5) Voila
As for your internet disconnecting every time the phone rings, is likely due to a damaged or missing DSL filter.
"The DSL service is sent through the main service line...However the signal will be feeding to all jacks... Filters are provided for these lines to block any interference that might be created by the DSL service." -wisegeek
Hope this helps, Good luck!