The LimeWire team does its best to answer questions on this forum and develop LimeWire at the same time. The "LimeWire reps" are the "software developers." Each one is a full time job, so until you invest a couple million dollars in the company so that we can hire more people, don't complain. It just gets old when we're all working very hard over here to meet users' needs and create as strong a product as we can.

The FAQ at:

http://www.limewire.com/index.jsp/faqs

addresses this question in detail. I also recommend uninstalling all previous LimeWire versions and restarting your computer before running the installer. The difference between 1.6 and 1.8+ installers is that the newer installer use InstallShield Developer 7, wherease the earlier installers used InstallShield Professional 6.3.