Each individual runs different programs on their computers. The choice to run them, or the way you set up the programs that I recommend, is totally up to your own discretion.
     The programs below are the ones that I recommend to EVERYONE.
     The 'daily and weekly' routines are the ones I follow myself.
     I go through a Complete cleanup of my customer's computers and instruct them
in the proper maintainence of them when done. This is how I keep my computers running at peak performance, and I rarely have computer problems from conflicts (and or) clutter.

Download, install and run
Disk Cleaner
Adaware SE Personal
Microsoft Windows Defender (previously known as Microsoft Antispyware)
(A valid copy of Windows XP with Service Pack 2 is needed to install this program)

Read and follow:
Increase Your Computer's Resources
Reset Internet Explorer Defaults
Daily Computer Cleanup Instructions
Weekly Computer Cleanup Instructions

Read: 10 Virus Detection & Prevention Tips!