You can use "Custom Actions" to add a new menu item to the ECB. See the "Add an Edit Control Block Menu Item" section on
this MSDN page.
You'd probably wanna do something like this (This works both in SharePoint 2007 and 2010)
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
<CustomAction Id="Task.Approve"
RegistrationType="List"
RegistrationId="107"
ImageUrl="Url of image of your menu item if any"
Location="EditControlBlock"
Title="Approve">
<UrlAction Url="Url of page to load when the menu item is clicked"/>
</CustomAction>
</Elements>