Need for Cleanup: Without periodic cleanup, computer will slow down, use up available memory, and eventually crash.

Things to Cleanup: Accumulation of Trash
Fragmentation of Disk
Unnecessary Programs in Memory
Corruption and bloating of Registry
Cookies

Cleanup Methods: Windows Software
Third-party Software
Web-Based Methods

B. Clean-Up Tools Available in Windows:

Scan Disk
Defrag
Clearing Recycle Bin
Deleting Browser Cache
Deleting Browser History
Add/Remove Facility

C. Third Party Recommendations:

Langa's Batch File (free) http://www.langa.com/cleanup_bat_novice.htm
Clean Sweep ($31 over the net or in stores) http://www.symantecstore.com/Product/0,1057,2-1-SN107254,00.html
Norton Utilities ($51 over the net or in stores) http://www.symantecstore.com/Product/0,1057,2-1-SN107064,00.htm
System Mechanic ($60 over the net or in stores) http://www.iolo.com/sm/index.htm
Evidence Eliminator ($75 over the net or in stores) http://www.evidence-eliminator.com
Cookie Pal (Shareware: $15) http://www.kburra.com
Cookie Viewer (free) http://www.winmag.com/columns/powertools/ptcookie.htm
Start-Up Cop (free) http://hotfiles.zdnet.com/cgi-bin/texis/swlib/hotfiles/info.html?fcode=000YKL&b=pcm

D. Web-Based Cleanup Tools:
PC PitStop (free) http://www.pcpitstop.com/
WinTune (free) http://wintune.winmag.com/?ls=wmnavwt