I would like to install a trial of AutoCAD 2014 on a client's machine to test it out and ensure that his computer is powerful enough before purchasing the license. If we decided that it's not, we'll be removing the 2014 trial. I don't want to come to this conclusion only to discover that installing the trial has permanently damaged/modified the 2005 LT installation.
I would install AutoCAD 2014 on a different computer. I would also check out the following URL to help you decide on your hardware requirements.
We don't have AutoCAD 2005 installed on any computers on the product support team so we can't comment if it will affected by the AutoCAD 2014 installation. Typically, we support the current version and 3 versions back.