Hi guys 
I'm new here. I had been reading a long time here on the forums but now I registered finally.
And got a question for you.
Since yesterday I've got successfully installed a X11-connection from my Windows Xp to a Ubuntu . Now there's a web portal needed.
So I have to make a homepage where are a few icons on it. If you click on one of those icons, there should appear a window with a X11-environment (like xming, cygnus).
Is there any possibility to do that? I've got absolutely no idea how to make this run... 
Hope you can help me...
Best Regards, Houssem
You'll need something to run server-side to identify the requestor IP address so it knows where to send the X11 session (or you'd need to accept an ip address entered on the web portal).
You'll also need to pass the web portal an xauth string (eg an MIT Magic Cookie) or to disable authentication on your X-Server (your display running on your windows XP box)
Then it's just a matter of making system calls on Ubuntu from inside a php or cgi script based on what button the user clicks.
Be sure to think about what unix user all this is running as, if it's the apache user, then make sure apache can interact with the files you'll need to see on the Ubuntu host.
Generally speaking, it's a better bet to use an X11 launcher (xming has one) that will run this stuff over an ssh session to the server for you - it will even let you make icons to run specific apps.