One of the most effective way of increasing your computer speed performance is to get an SSD. Even if your computer is old, using SATA 2, the SSD does worth! Check out this Real World Comparisons video.
In this article I will right away give an answer to the question, Is SSD worth it with SATA 2 or the 3 GB/s interface used by the older computers? The answer is definitely yes and you will see that in the following Real-World benchmarks and comparisons to a HDD.