Preventing spyware is a process of observation, familiarity and maintenance, as it is a technical one, things like low RAM, a badly fragmented hard drive, running many background applications or that fail to release memory after quitting, can all mimic the signs of viral infection.
A new PC usually has its operating system and anti-viral software or even a complete security package installed and some ISP providers also include these as a download or on their connection installation discs.
Prior to logging on to the net, run the anti-viral and anti-spy software.
Next step log on and download the latest security updates for Windows, and the anti-virus and anti-spyware. Ideally, they should be updated daily.
Processes running can be checked the using Windows Task Manager and as programs are added, they are listed and can be monitored in their behaviour.
More powerful third party applications like Process Explorer (Vista compatible) or Security Task Manager (currently not) give greater options.
Removal of spyware can prove difficult, as they can hide in areas like the system restore, or downloads other malicious programs, or alter the Registry as to not appear in the Add/Remove Program Panel,
Remove these changes in the Registry and create a log file which can be submitted to search engines and on spyware forums and message boards or the Uniblue Systems' WinTasks Process Library for analysis, by using HijackThis.
AVG is a competent virus killer, Spybot, Ad-Aware, and A-squared, deal with Spyware, Trojans and Root kits. Untested are IceSword, an anti rook-kit contender from China and Blacklight, another anti-root-kit application. Then download the following anti-malware applications, Microsoft's Malicious Software Removal Tool and Microsoft's Windows Defender. The Windows Automatic Update facility can be set to update your pc once a month.
These measures must be used with caution as they can cause instability or even crash the PC.