WinXP and secondary screen

[principher webspeed dk]

I am currently working on an application which should show some graphics on a fullscreen window in the 
secondary monitor. I have looked at the information on http://www.gtk.org/api/2.6/gdk/multihead.html, but on 
Windows XP (which is the primary development platform) the program returns that I have only one screen, 
eventhough I am quite sure I have two. :) Is there some other way of checking for and using the secondary 
screen in GTK.
The reason I want to use GTK is that I would like the program to run on Windows and Linux, Unix, MAC.

Hope there is someone who can help. 

Just for the completeness of information: I am using GTK 2.8.7 and has installed SP2 for WinXP. Unfortunately 
I do not have the possibility of checking if the sample code fails on other platforms aswell, since I do not 
have GTK headers installed on my Linux (for some reason they do not show up on my OpenSuse 10.0 eventhough 
the package manager says they are installed. Have to install GTK manually when I get time).