Back track is not a software, it is a "Linux" just like Ubuntu. To install the different software included in Backtrack Linux, just open software center, search for them and click install. That's all, nothing else to do.
If you want to install Backtrack itself, then download the ISO and overwrite Ubuntu or install it alongside. But please define "having a hard time installing". We can't help you if we don't know the issues you have. Also, please change your thread title to something a little more informative if you want peoples to actually click on it.