xfce4-battery-plugin : configure error

[Nicolas Fernandes]

Hi all !
First i'm noobs on this list so i just want to say THANK YOU to all the
xfce Team !! ;)

So, come-back to my problem :
 i use XFCE BETA on debian with a laptop and it's why i want to install
the battery-plugin but the release for debian don't work ! :(

So, i take source, untar and start ./configure and I take :

----------------------------------------------
...
checking for pkg-config... /usr/bin/pkg-config
checking for xfce4-panel-1.0 >= 3.99.2... Package gdk-2.0 was not found
in the pkg-config search path.
Perhaps you should add the directory containing `gdk-2.0.pc'
to the PKG_CONFIG_PATH environment variable
Package 'gdk-2.0', required by 'libxfcegui4', not found

configure: error: Library requirements (xfce4-panel-1.0 >= 3.99.2) not
met; consider adjusting the PKG_CONFIG_PATH environment variable if your
libraries are in a nonstandard prefix so pkg-config can find them.
-----------------------------------------------

How can i adjust the PKG_CONFIG_PATH ??

THX for help !

PS : sorry for my poor english ...i'm french :/

- Psy -