You need to defragment your PC by clicking Control Panel (Win 98 & XP) >performance & maintanance>rearrange items on your hard disc to make PC run faster.
Also frequently free up space on your hard disc which is above the option I just told you. Things many people don't know is when they browse the internet, websites put things in the the temp folder. To remove this right click on Internet Explorer>Internet Properties>Delete Cookies>Delete Files. In settings click on View Files then click on the yellow folder with a green arrow on it & you will see Temp Folder then delete everything.