Installation from ZIP archive
Just place PNotes folder wheresoever you want on your hard disk or flash drive. It is absolutely portable application, which does not require any additional settings in registry and does not leave behind any traces in registry as well.
Installation from other installers
Proceed accordingly to installer instructions.
Tip: if you are on Windows Vista or Windows 7 under restricted account - install it into root folder ("C:\"), instead of "C:\Program Files" (x32 system) or "C:\Program Files (x86)" (x64 system) in order to avoid UAC conflicts.