One of the most common problems with installing InaSAFE is, due to the large paket size of InaSAFE the downloading in slow(er) internet connections. If you frequently receive a timeout of your netwerk connection try to set Settings > Options > Network > Timeout for network requests to a higher number.
If you have no permanent network connection or you want to pass InaSAFE to friend who do now have an internet connection you can also install InaSAFE by manually downloading it from http://planet.qgis.org/plugins/inasafe/ by clicking on the latest version and then choose Download. This will get you the inasafe-x.x.x.zip file which you can afterwards extract in the plugins path of your QGIS installation.
If you have a copy of the plugin code in a zip file, you can install it unzipping it into the QGIS plugins folder. In Windows, it should be something like C:\Users\<your_user>\.qgis2\python\plugins. In Linux/Mac, it should be in ~/.qgis2/python/plugins. Copy the inasafe folder in your zip file into your plugins folder. You should end up having a .qgis2pythonpluginsinasafe folder with the code of the plugin and the required subfolders.
If your problems are still not solved you can write an email to email@example.com. We also have a InaSAFE User Mailinglist where you are very welcome to join and ask your questions there. More information about howto join the list is available on Getting Help.