I know the differences between linux and windows. I just want to have the visual of xp. Can this be done with 12.04, like it could be with the previous versions of (L)ubuntu?
Yes, it's possible to do that. All you have to do is find a theme that resembles Windows XP, or customize your own.
For the window background (GTK theme) and the icons (Icon theme), you can search at gnome-look.org for Windows lookalikes, for instance.
You can change the logo for the menu and the panel background. Just right-click them and open their properties. Then use the image you like best for that.
For the window title, you would have to find or create an openbox theme that pleases you. See:
I suggest Cinnamon Desktop. It has very similar visual layout to Windows GUI. It is still slightly buggy. I like this option because you can install it over regular Ubuntu. Instead of installing a different variety.
I recommend you also look into lubuntu because of it's wide user base and better support.
With my research you may have to create your own theme for any UI to get it to look like Windows xp as for layout.