Hi,
It depends on exactly where. Here are some starting checkpoints:
Go to Start/Run/Regedit and navigate to:
HKEY_CLASSES_ROOT\*\OpenWithList
HKEY_CLASSES_ROOT\*\shellex\ContextMenuHandlers
HKEY_CLASSES_ROOT\Directory\Background
HKEY_CLASSES_ROOT\Directory\shell
HKEY_CLASSES_ROOT\Directory\shellex\ContextMenuHandlers
HKEY_CLASSES_ROOT\Drive\shell
HKEY_CLASSES_ROOT\Drive\shellex\ContextMenuHandlers
HKEY_CLASSES_ROOT\Folder\shell
HKEY_CLASSES_ROOT\Folder\shellex\ContextMenuHandlers
Customizing Right-Click Menu Options in Windows
http://www.jfitz.com/tips/rclick_custom.html
ContextEdit lets you control which items appear on your context menu
(right-click) in Windows Explorer.
Add, Modify, Disable, Delete Context Menu Listings (Line 23)
http://www.kellys-korner-xp.com/xp_tweaks.htm