Thanks for your very useful reply. I first tried the Asus tool, but it won't work on non-Eee-PCs (and I own a Samsung netbook).
The french tool works nicely. They have rewritten the original "personalize" pages (with sometimes funny translations) of Windows and let you change your background, besides other personalizations.
I'll definitely donate 5 bucks to the author when the tool is stable and I won't run into any other problems.
Again, thanks for your help.