For everyone who has the same problem and needs a solution: i found it out myself.
You must update to linux kernel 3.3.0 to get initial support for the cintiq 24HD.
I found a guide how to install the new kernel without having it to compile yourself:
This guide will help you install Linux 3.3 Kernel under Ubuntu 12.04/11.10 or older.
For Ubuntu (i386 / 32-bit):
Open the terminal and run the following commands:
$ cd /tmp && wget -O linux-headers-3.3.0-030300_3.3.0_all.deb http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3-precise/linux-headers-3.3.0-030300_3.3.0-030300.201203182135_all.deb
$ sudo dpkg -i linux-headers-3.3.0-030300_3.3.0_all.deb
$ cd /tmp && wget -O linux-headers-3.3.0-generic_i386.deb http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3-precise/linux-headers-3.3.0-030300-generic_3.3.0-030300.201203182135_i386.deb
$ sudo dpkg -i linux-headers-3.3.0-generic_i386.deb
$ cd /tmp && wget -O linux-image-3.3.0-generic_i386.deb http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3-precise/linux-image-3.3.0-030300-generic_3.3.0-030300.201203182135_i386.deb
$ sudo dpkg -i linux-image-3.3.0-generic_i386.deb
For Ubuntu (amd64 / 64-bit)
$ cd /tmp && wget -O linux-headers-3.3.0-030300_3.3.0_all.deb http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3-precise/linux-headers-3.3.0-030300_3.3.0-030300.201203182135_all.deb
$ sudo dpkg -i linux-headers-3.3.0-030300_3.3.0_all.deb
$ cd /tmp && wget -O linux-headers-3.3.0-generic_amd64.deb http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3-precise/linux-headers-3.3.0-030300-generic_3.3.0-030300.201203182135_amd64.deb
$ sudo dpkg -i linux-headers-3.3.0-generic_amd64.deb
$ cd /tmp && wget -O linux-image-3.3.0-generic_amd64.deb http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3-precise/linux-image-3.3.0-030300-generic_3.3.0-030300.201203182135_amd64.deb
$ sudo dpkg -i linux-image-3.3.0-generic_amd64.deb
After you finish, reboot your system
$ sudo reboot
To check updated Linux kernel
$ uname -r
The output will show you the upgraded kernel.
WARNING
Please upgrade the kernel at your own risk because it may render your system unstable. Additionally, upgrading kernel may cause problems with some installed proprietary drivers of NVIDIA / ATI (AMD) graphics cards, broadcom wireless etc., so be cautious!
Now everything works the way it should be! =)