You will be happy to know that, within the KDE desktop, things work exactly as you would expect. Icons can be double clicked to launch applications, you can drag and drop in the file manager, KDE applications (such as KOffice) are fully aware of the entire desktop such that interaction between applications and the desktop is seamless, and the configuration/addition of elements works precisely as you have grown used to within the Windows XP desktop.
The elements are all similar. The action is similar. The look and feel is similar. Outside of the KDE Widgets (which add a dash of Apple OS X to the desktop), migrating from Windows XP to the KDE 4 desktop should be a complete no-brainer to even the newest user.