I use these  free anti-virus software, there are really good!

1.

http://www.avast.com/eng/home-registration.php

Welcome to the free registration of avast! Home Edition, the ultimate antivirus for home, non-commercial use. Both conditions should be met! For commercial environments, please use another product - avast! Professional Edition.

avast! 4 Home Edition works for 60 days after the installation in demo mode. You will obtain your FREE license key by E-mail after the registration. The license key is valid for 1 year. After one year you will need to just re-register.

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2.

http://safety.aol.com/isc/BasicSecurity/ 

McAfee^® VirusScan Plus – Special edition from AOL

Gives you the most comprehensive free set of safety tools available. We've partnered with a leading name in Internet security to deliver the essential protection you need:

• Virus protection guards your whole PC
• Spyware Protection blocks potentially unwanted programs
• Firewall helps keep hackers out

Since it's automatically on-guard and up-to-date, it helps protect you against today's attacks and tomorrow's threats, too.

Buy this protection yourself, and you could spend as much as $39.99, but with an aol.com email address, you can receive this comprehensive set of safety tools free.

3.

http://www.360safe.com/  Chinese web site

Get a free kaspersky from 360safe

Tweak hundreds of hidden features of Windows Vista, optimize your machine and customize it to your needs. The best tweaking software ever!

features:

• Activate hundreds of hidden Windows Vista settings

• clean your registry

• activate system and software restrictions

• display detailed system information

• create a 256 MB RAM drive

• protect your privacy

• clean your hard drive

• manage TrueType fonts

• improve your internet connection

• optimize your CPU

• optimize your RAM

• manage system updates, and much more ...

• you can even transfer your tweaks and settings to other machines!

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Heaps of free plugins are included with the freeware 'Basic Edition' of TweakVI. Additional plugins are available to subscribers and new plugins will be released from time to time once they become available. Subscribe today and immediately download up to 13 additional plugins for TweakVI!

Read the first review on TweakVI 'Basic' by Australia's APC Magazine.

See all details at: http://www.totalidea.com/content/tweakvi/tweakvi-index.html

 Symantec  listed Microsoft Windows as the most secure OS out there. They claim that Windows had the fewest number of patches and the shortest patch development time of any OS, including Mac, Red Hat Linux, Solaris, and HP-UX (any HP-UX fanboys in the house?).

But what make trouble is IE, so why not use Firefox base on the Windows system!

http://news.zdnet.co.uk/security/0,1000000189,39287981,00.htm

Apple has plugged around 100 vulnerabilities in OS X so far this year, but the malware threat to Mac customers is insignificant compared to users of Microsoft Windows.

you may have some horrible story about the using of Vista, please leave your story in the comment.

http://www.yelvington.com/20070722/i_hate_windows_vista

Google Toolbar for Firefox is a excellent extension for Firefox and Google lover. Its capabilities include extensive search options, spell checking, translation, pop-up blocking, highlightin, and more.

You can download from:     Google Toolbar

We use IE for so many years, it is so good to use it surfing the Internet. But from two years ago, I suggest people to switch to FireFox for security reason, because spyware and viruses can download,install and run on your computer if you still use IE.

 More people are interested in switching from IE to Alternative Browsers than ever before. See why they made the change and how easy it was. Discover the 101 features that Mozilla offers over IE 6.0. Learn all the great ways browsing the web with Firefox can give you a better digital life. And understand how firefox can make your life easier and your possibilities endless. http://www.switch2firefox.com/   

1. You'll only see porn when you want to.

2. Your kids will only see porn when they want to.

3. Your computer won't spend its free time telling the world about Viagra soft tabs.  see more go to:  http://www.killbillsbrowser.com/ 

The paging file (also called: Windows swap file or virtual memory file) is a system file that Windows uses when it runs out of actual RAM. If Windows memory is big enough, I suggest to disable paging file.

Defragmenting Your Drive,make sure your hard drive is properly defragmented.

disable System Restore
if you have a problem, you can restore your system to a previous state. Sounds nice, it even works, but the problem is that Windows uses huge amounts of your hard drive to save restore information from the day dot.

partly from: http://www.andreasroom.com/HowTo/WindowsOptimisations.aspx