Starting a script on xfce login and logout?

"If you have root access, you can always edit the startxfce4 script. According to the documentation:

startxfce4

The startxfce4 is a convenient script to start an Xfce 4 session from
the console. It will give you a
session with a taskbar and a panel and
with the desktop manager and window
manager running.

All programs, or symbolic links to programs, in ~/Desktop/Autostart/ will
be run by startxfce4 on startup.

To customize the behaviour of startxfce4, copy the file
${sysconfdir}/xfce4/xinitrc to your
personal ~/.config/xfce4/ directory
and edit that file. If you install
from source, ${sysconfdir} defaults to
/usr/local/etc; for binary packages it
is often set to /etc.

With the inclusion of a session manager in Xfce 4.2, the preferred way
to change startup behaviour is by
using the ""Save session"" option in the
logout dialog.

Or you can use the xfce4-autostart-editor program.

For the logout part, see the http://wiki.xfcedotorg/tips page for the personal logout script."