Most of the "help" requests I receive from friends and customers are to solve simple problems in their PCs. In many cases the problem is originated by "human factor" more than real bugs from the computer. Of course a lot of trubles are also related to viruses and spyware.
One good method to avoid that kind of trubles is by using the computer with an "account" without administrative rights. By defaul in Windows XP you are using an account with administrative rights.. so it allows viruses and spyware to be instaled on the pc. It also means that the user of the computer can install any program from internet that could be infected with viruses or that include spyware... so that's bad.
My advise for non experienced users is to create an account without those administrative rihts. Windows XP makes it easy:
Step 1: Open the Control Panel
Step 2: Select the option of "User Accounts"
Step 3: Select the task "create account"
Step 4: In the new window specify the name for the new account. It can be the name of a user or any word that goes good for what that account will be used for
Step 5: Select the "Limited" account type and then press the "Create Account" button
And that's it! you can restart the PC so you will se in the welcome screen the new account. If you wish you can setup a password for this account.
I advise you to read the following article from PC Magazine. There you will find more details and warning about this way of securing your PC.