The fastest, cheapest, and easiest thing you can do is add more memory (assuming it doesn't have more than 1GB of memory now). If you take an old PC with 512MB of RAM and upgrade it to 2GB of RAM you will notice a HUGE difference with no other changes. I just did this for someone that had a very old PC with 384MB of RAM (128 + 256). It was ready for retirement but they refused to let it go. It was running Windows Home Edition and it was slow as a dog (although surprisingly uncluttered). I could tell they didn't use it much. I looked up the specs for the PC on Dell.com, determined the type and maximum memory that could be installed (2 GB - two 1GB sticks of memory). I purchased the memory through Amazon.com for $80 and when all was said and done they could have swore that they had a brand new machine.