Writing Code Behind for MenuItems defined in Custom Action

A)

When ever you want to  add the application page to Particular location in sharepoint site
Get the reference of this site
http://www.customware.net/repository/pages/viewpage.action?pageId=69173255
for example

To add code behind, You need to inherit  the class from MenuItemTemplate, and to Capture the Postback events inherit for Interface IPostBackEventHandler
public class MyListSiteActionMenu : MenuItemTemplate, IPostBackEventHandler
{
public MyListSiteActionMenu()
{
this.ID = "myOwnIdHura";
}

protected override void CreateChildControls()
{
this.Text = "Delete Item";
this.Description = "Deletes Item";
this.ClientDEFANGED_OnClickPostBackConfirmation = "Are you sure you want to delete this item?";
this.ClientDEFANGED_OnClickUsingPostBackEvent = this.ID;
}

public void RaisePostBackEvent(string eventArgument)
{
SPContext.Current.ListItem.Delete();
SPUtility.Redirect(SPContext.Current.List.DefaultViewUrl, SPRedirectFlags.Default, this.Context);
}
}

Some more links  adressing postbacks of  Menuitem template
http://www.dev4side.com/community/blog/2010/3/9/implement-postbacks-in-the-spmenufield-sharepoint's-control.aspx

B)Modifing the text of the MenuItem depending on  Custom List Property value
in 

Psedo Code as follows
CreateChildControl()
{
 //Code to display text of  menuitem depending on Custom List Property value
set the text of menuitem  according to property of list 
} 

RaisePostBackEvent(string eventargument)
{
//updated list Propery on menuitem click
list.rootfolder.Addproperty();
list.rootfolder.SetProperty() ;
}