I live with people that rely on Windows for production use, so I can't really get them to use Linux. So I have to make do with Windows, Windows XP to be exact. I tried Vista before (for quite a long time - not just 20 minutes or something like some people do) and I hated it..

Stopping viruses getting in

Comodo Internet Security: Does a good job at keeping out nastiesViruses aren't really a problem with Linux, so you will be safe with Linux (at the current frame of time anyway). With Windows, it has been a problem for a long time, and this has gotten companies making antivirus, antispyware etc. software. My most favourite free one is Comodo Internet Security. It used to be just a firewall, but it has now expanded to become an all-in-one suite.

To be secure, you've got to tell the user about almost everything that goes through. This is kind of like UAC, but less annoying. Comodo likes to ask you a lot of questions when something happens, like during an update or when you install something. A little box in the bottom right hand corner appears saying "Some program is trying to access ... " and you have to block or allow it. When installing a program, you must select "Install or Updater" mode, otherwise you will be constantly prompted every time a file is installed to the computer.

Limited user: Being limited can stop viruses being as effectiveThis program has worked pretty well, but that alone doesn't really work too well. Setting everyone to a limited user except for one can really help. Set a user that you don't use very much and install programs with that user. Using an administrator account for daily usage can be very dangerous, like logging in as root in Linux.

It also stops people installing dodgy programs. Searching for a program on Google can give you programs which may include more than what it says on the tin (hint: probably viruses!).

Keeping things up to speed

When you install Windows, it can whizz past even some of the speediest Linux installations. Unfortunately, it gradually slows down...and down...and down, eventually down to a crawl if you don't do anything.

Defragmenting

Jkdefrag: A good alternative to the built in defragmenterPretty much any Windows "power user" will know about defragmentation. Your hard drive gets fragmented becuase the filesystem Windows uses, NTFS, is "lazy". It just dumps all of the information on top. It then gets split up everywhere, making it take longer to access something.

It can take quite a while, especially if your hard drive is big. Be sure to use a different defragmenter, because the built in one isn't very effective. Jkdefrag is a good alternative.

Cleaning up after it

CCleaner: Cleans just about anythingWindows leaves a lot of mess around. Things like caches, temporary files and other files are left lying around wasting precious disk space. The built in "Disk Cleaner" is adequate for the job, but CCleaner is even better. It is quite annoying that it tries to install Yahoo toolbar when you install it, but just watch out for it when you're installing and you won't have an annoying toolbar wasting your screen estate.

It can clean just about anything. It cleans almost all web browsers, Windows Explorer, Foxit Reader and more. Just look in the "Other applications" (or something like that) and you'll find it can clean even more programs.