This type of problem is almost always hardware related. Keyboards can be cleaned. It is probably dirt related, or wear related. Simplest thing to do is (with the power off on the system) take a firm hold of the keyboard, turn it up side down, and give it a good shake. You may be surprised as to what will fall out. Opening it up may be the only way to clean the internals properly. If you are not skilled at this, you may find you wind up with parts all over the place; so be careful.
You can disable keyboard repeat in KDE, and I would bet there are ways to do it in gnome and most other desktops. In KDE, go to Start --> Preferences --> Control Center and look for the keyboard. There is a check box to disable keyboard repeat.