I like your sig, early 70's pop rock guy.
A few more thoughts.
While your computer is disconnected from the internet, any application that tries to access the internet will interfere with stuff you're doing in the "foreground". IE, if your computer is just sitting there disconnected and you then launch IE, your computer will launch the dial up networking application. Other applications can have the same effect, but hidden from view. The point is, make sure that anything that would try to get at the internet (like Outlook, other email clients, IE, other browsers, etc) are off, not running, have no icon in the system tray, etc.
My further guess is that the driver installation installed and launched some piece of internet-aware SW that started to run during the installation, which triggered the dialup. The only reliable way I've found to defeat this is to delete the dial-up networking connection itself from your networking properties (not the protocol or adapter, but the icon containing the phone number and stuff.)
If Jim's suggestion doesn't pan out, come back and tell us what model of cable modem, are you connecting it to USB or ethernet,is there a router involved, etc. Right now "we know notheeeng!"
Also, do "ipconfig /all" at the command line and paste the listing into a message here as a diagnostic...