Services You Can Disable (In Vista)

There are several services you can disable to help improve performance.

Desktop Window Manager Session Manager - Provides Desktop Window Manager startup and maintenance services.
If you don't plan on using Aero Glass, you can disable this service.

Diagnostic Policy Service - Enables problem detection, troubleshooting and resolution for Windows components
Set to Disabled

Diagnostic Service Host - Same as above

Diagnostic System Host - Same as above

Offline Files - The Offline Files service performs maintenance activities on the Offline Files cache, responds to user logon and logoff events, implements the internals of the public API, and dispatches interesting events to those interested in Offline Files activities and changes in cache state.

Terminal Services - Allows users to connect interactively to a remote computer. Remote Desktop and Terminal Server depend on this service. If you don't use either of these, then you can disable the service.

Windows Error Reporting Service - Allows errors to be reported when programs stop working or responding and allows existing solutions to be delivered.

Windows Search - Formerly this was the Indexing Service. Provides content indexing.

Changing the Sidebar (In Vista)

By default, the sidebar can take up a unwanted room on the desktop. You also can't put icons on the space it uses.
If you want to retain the ability to display the sidebar gadgets but also want full use of the desktop,
you can detach individual gadgets.

Right-click the gadget you want to detach
Click Detach from Sidebar
Move the gadget wherever you want on the desktop
Right click on the sidebar
Click on Close Sidebar
There will now be an icon in the system tray for the sidebar if you want to get it back

GUI Performance

You can turn off some of the eyecandy to help speed of graphics performance

Open the Start menu
Right click on My Computer
Select Properties
Click on Advanced System Settings
In the Performance section, click on the Settings button
Click on Custom
I usually only have:
Show preview and filters in folder,
Show shadows under mouse pointer,
Show thumbnails instead of icons,
Show window contents while dragging,
Smooth edges of screen fonts,
Use drop shadows for icon labels,
Use visual styles on windows and buttons

Access Denied to Folders

If you are getting Access Denied errors when trying to open folders like Documents and Settings, Application Data, Local settings:

Right click on the Folder
Select Properties
Click on the Security tab
Click on the Advanced button
Click on the Owner tab
Click on the Edit button
In the Change owner to box, highlight your account
Check Replace owner on subcontainers and objects
Click on Apply
Click on Yes to replace all permissions
Continue to click on OK until you