"computers themselves don't get slower. It's just that as time goes on people with little experience with PCs start downloading a bunch of programs that run in the background. That and hard-drive fragmentation.
Here's how to keep your PC as fast as it can get:
- Avoid anti-viruses like the plague.
- Keep background processes (CTRL+ALT+DELETE and hit the processes tab) under 20 when playing a game.
- Run Spybot : Search and Destroy every once in awhile.
- Defragment your hardware on a regular basis."
From a Game spot
Heres the link that claims vista doesn't really need anti virus
Quote from security site below
""It's no secret that most malware targets Windows-based machines. Microsoft recognized this fact a long time ago and addressed the problem by incorporating several types of anti-malware technology directly into its Windows Vista OS.
Key to Vista's virus-fighting capabilities is UAC (User Account Control), which automatically senses potentially dangerous situations and temporarily suspends running programs and processes, effectively trapping any malware that may be trying to install itself on the machine or run itself with administrative privileges.
Windows Defender also protects Vista PCs by working to keep the system free of many types of malware, including spyware and adware. Windows Firewall, meanwhile, blocks suspicious types of incoming and outgoing traffic, greatly enhancing system security. The automatic-updating feature provides yet another layer of protection by ensuring that the host system is kept up-to-date with the latest security patches and enhancements; this feature does not require the user to take any action.
The Verdict: The combination of UAC, Windows Defender, Windows Firewall and automating updating does a very good job of keeping Vista-based machines secure. Unless a Vista user is inclined to perform foolish actions (such as intentionally subverting UAC and other security-oriented services), external anti-virus protection is usually unnecessary. However, downloading lots of software via Web sites, torrents or email can get users into the kind of trouble that these built-in protective features can't protect against.""