1. download Google pack. it will give you give you spyware doctor with can help speed up your computer by detecting viruses that cant be detected by other virus scans or you will have to wait till the end of the scan it also has a Norton Security Scan witch detects other viruses. it has Firefox it allows  you to  brows the web at a faster speed than internet explorer. it also has RealPlayer, Google Photos Screensaver, Picasa version 2, Adobe Reader, plus if you dont have Microsoft office, donload StarOffice 8, it’s a imitation of  Microsoft office programs.
2.DO NOT install Google desktop on a PC with vista. it will create a problem with windows  side bar.
3.if you have not done a defragmented recently do so.
4.do a disk cleanup it will give you more space on your HDD. and might help speed up your PC slightly.
5.if the computer is old and is running slow change the view to a classic view or disable all unnecessary animations. how you do so is go to control panel when on the classic view click on Ease of Access. then click on make it easer to focus on a task. when there pet a check on turn of all turn of all unnecessary animations. then click save.
6.Google web accelerator will speed up your web browser speed but it will cause Firefox to slow down.
7. index all your files on the computer so you will be able to search faster.
8.if you have something like dell automated pc tuneup do it if you are not on a administrative account it will not do everything it was meant to do.
9.get a program like PC DOC PRO or a other registry cleaner do a scan so and fix any errors.