1. The Disk Cleanup tool
This helps you free up space on your hard disk by searching your disk for files that you can safely delete. You can choose to delete some or all of the files. Use Disk Cleanup to perform any of the following tasks to free up space on your hard disk:
- Remove temporary Internet files.
- Remove downloaded program files. For example, ActiveX controls and Java applets that are downloaded from the Internet.
- Empty the Recycle Bin.
- Remove Windows temporary files.
- Remove optional Windows components that you are not using.
- Remove installed programs that you no longer use.
2. AusLogics Disk Defrag
Disk fragmentation leads to system slowdowns, PC crashes, slow startups and shutdowns. Auslogics Disk Defrag is designed for fast optimization of modern hard disks.
3. Spybot - Search & Destroy
This software detects and removes spyware, a relatively new kind of threat not yet covered by common anti-virus applications. Spyware silently tracks your surfing behaviour to create a marketing profile for you that is transmitted without your knowledge to the compilers and sold to advertising companies. If you see new toolbars in your Internet Explorer that you haven't intentionally installed, if your browser crashes inexplicably, or if your home page has been "hijacked" (or changed without your knowledge), your computer is most probably infected with spyware. Even if you don't see the symptoms, your computer may be infected, because more and more spyware is emerging.
4. Ad-Aware
Ad Aware is a very powerful anti-spyware tool! It provieds real-time protection against spyware, trojans, rootkits, hijackers, keyloggers, etc!
Use these programs as part of your regular maintenance and you will avoid many major problems.
Technical
Tips 
Dr Daves Mobile Computer Services strongly recommends setting up the following four icons in a prominent place and using them on a weekly basis to immunise your computer against potential viruses and threats.