Instead of having to open your internet browser to use InsaneJournal, you can get a downloadable client from [http://www.livejournal.com/download/]. A downloadable client will allow you to conveniently update your journal, manage your friends list, and use other various features.
By default, most of those clients have LiveJournal.com as their server. In order to use them for InsaneJournal, you will need to modify the settings and replace the references of LiveJournal.com with InsaneJournal.com.
Please note that in order to use a client, you must already have an InsaneJournal account. If you don't have one, you can create one for free by visiting [http://www.insanejournal.com/create.bml].