On occasion Get rid of programs that start up in the system tray.
Daily/ Hourly Update virus definitions
Weekly Favtool
rdisk /s
Backup your data directory
Run Ad-aware
Scandisk hard drives
Monthly Run FavOrg
Download critical updates
Defragment hard drive partitions

On occasion

Get rid of programs that start up in the system tray.

Start > Run > regedit

Browse to the following two branches:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

Save a backup copy of this branch.
Highlight the Run folder(branch)
Registry > Export Registry File
Save as type: Registration Files
Filename: c:\{pick a safe location in case you have to restore}\run_branch
Export Range: Selected branch: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

Figure out what each program does.   You can do this by searching the hard drive for each filename.  If it is something that you do not need running all of the time, then delete it.   This will prevent these programs from launching themselves when Windows starts, and help you by increasing the system resources.
 

Daily or Hourly

Update virus definitions - I was using Trend PC-Cillin.   I have the software scheduled to check for new definitions daily.  This software does not have the option to check hourly. Now I am using AVG. They have a free product, and it is pretty good.

This is not an ideal setup (click here for the reason why).
 

Weekly

Favtool - Export IE Favorites on a daily/weekly basis to D:\Data\{your username}\IE favorites.

rdisk /s - Create Emergency Repair Disk -

The "/s" means "Updating (Saving) the Repair Info" copy the c:\winnt\repair directory to CD-RW disk for backup of registry.   To restore registry, boot to different hard drive that can read/write NTFS.  Expand the files in the winnt\repair directory by using expand.exe.   Copy the files from filename._ to filename.cab.  Run expand filename.cab filename.   This will expand the registry file.   Copy to the appropriate directory.   Most will go in \winnt\system32\ or winnt\system32\config.   The ntuser.dat will go in winnt\profiles\default user\.

Backup your data directory - I am backing up my core data to CD-RW disks.   You can also back up to tape, or some other removable storage medium.   It is good to keep the backup in a geographically separate location than your computer.   In case of natural disaster, and your house/business is wiped out, you will be able to restore your critical data from your backup copy.

Run Ad-aware - This program will get rid of Spyware software.  Spyware programs are sometimes installed with other software packages, and they keep track of little things about you without you knowing it.    It is also important to download the latest version of Ad-aware or just the Ad-aware signature file from time to time to make sure that you are scanning for the latest Spyware programs.

Scandisk hard drives  - Kill all processes that may be writing to the drives before running, otherwise you will get error "windows was unable to complete the disk check"
Scandisk /autofix /nosave /surface
 

Monthy

Run FavOrg to download all of the IE Favorites Icons (favicons).   Normally when you browse websites, the Favorite (bookmark) icons get saved in the disk cache.   This means that they are automatically purged over time.   The FavOrg program will store these icons in a more permanent fashion, and it also has some cleanup tools for the Favorites (bookmarks).

Download critical updates from Microsoft, as well as Set up Critial Patch notification
http://windowsupdate.microsoft.com/

Defragment hard drive partitions - Install Diskeeper Lite 1.1.137.   For each partition, double-click on Analyze.  It will check the partition and tell you how fragmented it is.   If the partition is sufficiently fragmented, double-click Defragment.
 

Run freeware virus scanner.

Note: Many of these online scans won't work with a secure browser like Firefox, so you will have to use an insecure browser like Internet Explorer.