I am a Ubuntu user and hence these instructions are for a PC with Ubuntu as the OS. Windows users are on their own.

1. Download the .deb file to your PC.
http://www.lexal.net/NuvoBlack.deb

2. Right Click on the downloaded file and click "Extract Here". The file gets extracted to a folder called "NuvoBlack.deb_FILES"

3. Browse to the folder and you will see a file called "data.tar.gz". Right click this file and extract again. The file gets extracted to a folder called "data.tar.gz_FILES"

4. Browse to this folder and you will find 2 folders one named "home" and the other named "usr" These are the 2 folders that need to get copied to your N800.

5. Attach your N800 to the PC using the USB cable and copy these files to your N800 SD card (Internal or Removable). Unmount your N800 drives and unplug the N800.

6. Assuming you have ssh, become root and xterm installed. Open xterm. Type "ssh root@your_N800_ip". Enter yor password. Once your are logged in as root type "cd /media/mmc1" or "cd /media/mmc2" depending on where you copied the files. A quick "ls" in xterm will let you know if you are in the right place.

7. Type the following into xterm

cp -rfp usr/share/themes/NuvoBlack/ /usr/share/themes
cp -rfp home/user/.opera/skin/NuvoBlack.zip /home/user/.opera/skin/

8. Exit xterm. Now select NuvoBlack from themes in control panel