We recommend the following free resources available from the Internet:

Avast! AntiVirus FREEAvast Home Edition is an excellent free antivirus - well worth a download.   Zone AlarmZone Alarm Free is a good firewall for those on XP. 
Vista and 7 both have excellent built in firewalls.
Trend Micro HousecallTrend Micro Housecall is a good free online virus scanner. Only a small download, and works alongside your currently installed anti-virus.   OpenOfficeOpenOffice is a direct replacement to Microsoft Office. Completely free, and compatible with Office.
GIMPGIMP is a powerful graphics editor to rival the industry leader, Photoshop, but it's free! It is rather complicated to learn though.   IrfanViewIrfanView is a simple graphics viewer, with some basic editing options. Great for minor changes to your holiday photos etc.
AdAware FreeAdAware fights internet nasties that your anti-virus doesn't see as a risk, such as tracking cookies etc. Useful addition for any computer system. Make sure you get the free version.   CCleanerCCleaner allows you to clear up your PC's temporary files automatically - and even cleans up your registry for you.
VLC Media PlayerVLC is a free Audio and Video player that can play virtually any audio or video format without the need for additional codecs.   CNET DownloadCNET is a great website, with a vast collection of freeware, shareware and full paid-for software. Each piece of software comes with reviews so you can see what your downloading.
Advanced System Cleaner FREEAdvanced System Care Free is a good FREE system checker and registry cleaner.    

Freeware: A piece of software that's free to use - sometimes you can only use it free if your a home user. Often a cut-down version of the full package, and sometimes comes with "nag-screens" asking you to download and buy the full package.

Shareware: Software that's free to download and try. The authors of the software accept payment from you in return from using their software, but unlike other software, you only need to buy it if you use it - so they are great to download and try. Most shareware won't expire if you don't buy it, but it's "etiquette" to pay for it if you use it.

Trialware: Many software packages now come with a "try before you buy". Similar to shareware in some ways, but generally Trialware will expire after the set period (normally 30 days). Major software houses, such as Apple and Microsoft use this system for their new software.