hi,
most of the plugins and zscripts you downloaded…the threads themselves explain how to unzip and place them where they belong. You can see my worlds best link below to find em quick and follow their directions.
as for the models…i created a new folder within the zbrush folder for myself to keep track of models…then created two more within that one…one for my stuff and one for all the generous donations from others to experiment with. How you do it is up to you tho.
regular zscripts that are not plugins can just be copied right to the zscript folder within the pixologic/zbrush2 folder.