You can't get the support page to work? That's not a good sign.
This could be anything, but it's most likely something not healthy on your machine. The test I would do is make a new admin user account. Then log in to that account, launch IE and try to install ADE to that new account. If that works, then your regular login profile is in bad shape..
You can also open a case via that account.
To open a Digital Editions 1.5 Technical Support case, please use the contact links at http://www.adobe.com/support/digitaleditions. If you can't open the page on the new account please provide more detail about the behavior you're seeing.