Windows XP supports transparency, which can be applied to your desktop to obtain attractive effects. One of them is having a transparent taskbar that almost blends with the desktop Wallpaper.
With Transbar you can easily apply this effect on your own computer. Simply launch the program and select the percentage of transparency you'd like to have.
You can see the results in real time! Also, the program can be set to be run at Windows startup so that you don't have to manually change it every time you launch Windows.
Just one tip: be aware of the folder where you install Transbar. My copy decided to install itself in some really deeply hidden folder instead of the standard Program files and, as I didn't notice it, I spent some time looking for it.