That depends. How much time do you have? Although a replacement keyboard is easy to come by the keys are much harder to find. Even though all of the replacement keyboards for a particular laptop look alike and connect to the laptop in the same way, the method used to connect the keys to the laptop keyboard is very different keyboard to keyboard. That is because one model laptop may have as many as 6 different keyboards. They all look the same on the surface but each is different when it comes to keys.
The Dell Latitude D620 keyboard is a great example. The keyboard itself is simple to install and any keyboard from any Dell Latitude D620 will easily fit another D620. They keys are not nearly as interchangeable. There are 6 models of keyboard for the D620. Each keyboard has completely different keys giving you less than a 17% chance the key you get will fit.
You are much better off buying a complete replacement laptop keyboard. They are much easier to find and install.