It looks InstallAware may cripple your Internet Explorer setting a low value in HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings, ReceiveTimeout. It could be set to 10000 (10 seconds), and that will make Internet Explorer timeout and show its very little informative "Page cannot be displayed" message (it never says why it wasn't able to load the page, if it was a timeout, an unreachable address or whatever).
I have InstallAware 9 and Delphi 2010 Ent. installed, and had that key. My colleagues with Delphi 2007 installed have not that key. My system at home with D2010 Pro installed never had problems, I didn't check for that key yet, thereby the culprit looks to be InstallAware itself.
Deleting that key, or setting it to a much higher value will make IE work again. The symptoms are that while IE will timeout often with slow responding sites, other browsers (Firefox, Chrome, etc.) will work without any issue.
Thanks to these pages for helping to solve the issue:
This Microsoft Support article (181050) says that the default timeout is set to 60 minutes from IE5 onwards. I wonder InstallAware developers decided to change a user-wide setting to solve a problem of theirs, instead of looking for a proper solution, but despite some nice features, there are many reports about InstallAware lack of proper behaviour.