At a customer site we did have a problem installing IBM Connections 4. The customer had installed the Websphere node without an default application server. This should normally not be a problem as the application servers for Connections will be installed by the Installation Manager later..
In the IBM Connections Installation Manager there is a panel for the Cognos installation. If you do not want to install Cognos at that time, you should be able to just enter a dummy user/password and press the "Validate" button. Even if the validation is not successful you should get the "Next" button to go forward to the next panel.
However: If your node,,into which you want to install Connections, does not yet contain an application server, the Installation Manager is unable to read the value for the port number from the application server profile. And without a port number you are unable to proceed to the next panel.
As a workaround you need to close the Installation Manager, create a dummy application server via the Integrated System Console into the node where you want to install Connections, and then start the installation again. Now the Installation Manager does find the server profile and can read the port number from there and you are able to proceed.
After your installation has been completed you can then delete the dummy application server again.
This is for sure a bug and IBM Support will write a technote for it (and hopefully this will be fixed in the next release as well ;-))