PeaZip is a natively portable standalone application, requiring none or minimal installation on the target system.
This is an advantage when it's desired to have a portable application to just unpack and run, or when a library freeze is desired and shared libraries should not be furtherly changed (i.e. on some production system), or when it's desired to have a single application with almost identical look and feel and features in an environment with mixed systems or desktop managers.
One obvious shorthcoming of this approach is scarce system integration on target environments; FreeDesktop standars (http://freedesktop.org/wiki/Standards/menu-spec) however offers powerful and easy to use methods, using .desktop file scripting, for integration of applications in desktop environments following FreeDesktop standard guidelines (notably, Gnome and KDE).

With following instructions you can easily integrate PeaZip with Gnome and KDE:

1) copy PeaZip's folder, or better link peazip binary, in one of the system's binary folder i.e. /bin or /sbin or /usr/bin (recommended) or any path fit for your system;

if using Gnome:
2) copy .desktop files in /usr/share/applications
3) optionally you can customize .desktop files in order to use PeaZip's icons for Linux (see peazip_icons_linux.zip package on SourceForge): place the icons in /usr/share/icons and change consequently the "Icon=tar" entry in .desktop files.
NOTE Gnome is often configured to use /usr/share/application and /usr/share/icons paths as in the example (i.e. on Ubuntu), but the paths may be different on some distribution or in some specific installations.

if using KDE:
2a) copy peazip.desktop file in (kde directory)/share/applications/kde if you want to add PeaZip in KDE start menu (and 'Open with' dialog);
2b) copy other .desktop files (each one performing a separate action, i.e. add to archive, extract here etc...) in (kde directory)/share/apps/konqueror/servicemenus if you want to add main PeaZip's functions to Konqueror's context menu: single or multiple files (of any type) and folders can be sent to PeaZip which will then determinate the action (open or add to new archive) depending on file type (i.e. as for extraction, PeaZip is able to extract multiple archives, even of different types, at once in parallel);
3) optionally you can customize .desktop files in order to use PeaZip's icons for Linux (see peazip_icons_linux.zip package on SourceForge): place the icons in (kde directory)/share/icons and change consequently the "Icon=tar" entry in .desktop files.
NOTE (kde directory) vary from distribution to distribution (or can even be customized by the user at KDE installation); /opt/kde3 is usually a common place for installing KDE and is used, in example, in Suse and OpenSuse. The (kde directory) is specified in $KDEDIR in environment variable and can be overridden by $KDEDIRS.