2 Things I did that really improved my PC's performance
Visual Effects/select Adjust for Best Performance
Advanced/Virtual Memory/select Change/On my main Hard Drive ("C:") I increased Initial Size from 750MB to 1000MB and also increased Maximum Size from 1500MB to 2000MB.
This turns off the video processing fancy bells and whistles that slow down processing and take up memory resources and increases the amount of processing power and memory available for the system to use.
By my own personal estimate doing the above seems to have increased overall speed and stability by around 20-25%.
Programs launch faster and web pages load quicker.
Running a 5 year old Dell Dimension 5100 on a P4 processor with Windows XP Home with 500MB of memory.
Browser is either Google Chrome or Firefox, sometimes Internet Explorer.