Question: I recently reinstalled the OS (Windows XP Home) on a friend's heavily spyware/adware infected machine. It appears as though his kids (7 and 11 years I believe) were visiting sites that offered downloads for search bars, screensavers, and "cute" cartoony animations that anyone with safety in mind would never download.

Some of the concerns I noted on the machine were:

* The main account was Administrator
* Expired anti-virus software
* Lack of Windows updates
* Multiple firewalls installed

Basically, I'm looking for a guide for non tech-savvy users that would help them avoid getting infected again.

Answer: 
* Have non-tech users accounts be non-admin
* Teach safe browsing habits
* Never download anything that isn't from an 'official' source
* Use Firefox/Chrome/Safari/Opera instead of Internet Explorer
* Run malware scans regularly
* Set Windows to update automatically
* Install virus protection and scan automatically/regularly
* Install a firewall
* And again, smart browsing habits.

For firewall, either don't use one (and use Windows Firewall instead) or install one free one, like ZoneAlarm.

Edit: I see in your question you mentioned expired anti virus. Use AVG instead. It's free and will never expire and updates automatically.

Edit2: As others have mentioned, you could install software that basically locks the computer down. I have to disagree with this. I would much rather take the time and teach the users (especially the children) about how to properly use the computer to the fullest, rather than block them out.
Here is a simple answer:

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> Avoid using the Internet.
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> 
> 

And another simple answer:

> 
> Don't install *anything*.
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>