"About this mac" not showing a black window

[Injerto]

Hello. First of all, I want to thank all the endless help this forum gave me, as I couldn't had become a Mac user without it. I'm using OSX 10.5 as my only OS since April 2009, and yesterday I did a step forward to 10.6. Its been a pain, an entire night without sleeping, almost 20 reinstalls from scratch, endless testings and a lot of reading. But its working, from the network connection (Atheros) to my video card (ATI Radeon HD4850).

 

I just have a little concern: my "About this mac" looks just like in OSX 10.5, instead of black-backgrounded as it should:

 

 

What could this be related to? The first time I installed this version, it did look blacky, but after so many reinstallations I can't see where did I do something that could have changed its behavior. Any clue?