It took me some time to figure out how to get appropriate dump on 64 bits boxes using adplus tool. Thought to share out it you:

1) You can use following CFG SCRIPT for capturing dumps StackOverFlow exception

<ADPlus>
   <!-- Add log entry, log faulting thread stack and dump full on first chance StackOverflow -->
<Exceptions>
     <Config>
        <!-- Use sov for stack overflow exception -->
       <Code> sov </Code>
       <Actions1> Log;Stack;FullDump </Actions1>
       <!-- Depending on what you intend - either stop the debugger (Q or QQ) or continue unhandled (GN) -->
       <ReturnAction1> GN </ReturnAction1>
     < Config>
  </Exceptions>
</ADPlus>

Save that as ADP_w3wp_Crash.cfg in location(Default is  c:\Program Files\Debugging Tools For Windows)

Run it as :
   cscript adplus.vbs –crash -p <ProcessID> -o c:\dumps -c ADP_w3wp_Crash.cfg

2) Use the following cfg file for capturing dump on NullReferenceException

Save that as ADP_w3wp_Crash.cfg in location(Default is  c:\Program Files\Debugging Tools For Windows)

Run it as :
   cscript adplus.vbs –crash -p <ProcessID> -o c:\dumps -c ADP_w3wp_Crash.cfg

Happy debugging