Few days ago, I installed Kubuntu Linux on my computer, but... it's hard to change it's appearance, scroolbars, buttons.. Can you tell me what Linux (RedHat, kubuntu etc, but free! I should choose for the easiest customization and changing appearance?

Desktop appearance doesn't depend on the distribution!  
I explain :
Changing scrollbars, buttons, ... are due to your Desktop environment.
Each distribution has a default one , but you can change i without changing your distribution.  

Kubuntu's desktop environment is KDE.
Maybe try Gnome (Ubuntu's default desktop) or Xfce.

Each desktop environment let you the choice between different themes.  

   Installing Gnome on Kubuntu  

I prefer Ubuntu too..
Its quite easy to use.. and costomize

And it's the cleanest and most professional

You don't choose a distribution but an interface ...
Gnome ( Ubuntu, Fedora ), KDE ( kubuntu, Mandriva) , xfce (Xubuntu)
and now we have the 3D interface, Beryl or Compiz with their effects .
I started with Debian and now I use Ubuntu because Debian is so boring to install :-)

Gnome is good -> install Ubuntu or Fedora

this 2 systems are different about the software installation process but the forum of this OS explain all U need to know

sorry for my english, i'm  french lol

If your willing to hand out some dough, go for Linspire

You can use Linux Distribution Chooser to help you to find your best   solution

Wow! That Linux distro chooser really works  ! Thanks YellowMan!  

read my response in what is your linux os section- that asnwers all and why.

i'm also looking for an easy to use linux. as i read in other thread ubuntu should be good

Yes, Ubuntu is easy and works well. I would suggest it to you.

You can also try Fedora  Its cool tooo

This is a pretty old topic. No need for new suggestions

Ok boss!!

abit late but i reccomend ubuntu !!!!! way better than xp

---------------