Hey amy thanks for a great mod I just made some minor modifications to your product so I thought I'd share. Strangely, I only got it to work if i made the mods to the plugin portion before install.
If anyone needs them to get them to work properly on their forum let me know and i can get it working for you.

I am going to work on a version of this with options in the Admin cp using your mod and Sina's mod i think i can hash something together

if you want this to work only after email verification and/or after they finish registration when email verification is disabled then use the edit i just posted
if you dont want the welcome template changed from what you made it then use the one contained here

I've a question. My new thread is popping up under the username of the new member, and not the 'general staff' username I created.

In the list of threads it looks like the user has posted a thread to welcome him or herself. Once you open the thread, the username is the 'general staff' username.

I don't know where in here:
To fix that?

Should I change $username to the UserID of the 'general staff' that I want to use ?

I got it, thanks! Great hack!

great, thanks Amy :)

What's the difference to your minor modifications lil7rocket?

Does this work w/ 3.6 ?

yes it does!

Can this be made to post a new thread (or a new message in an existing thread) when (and only when) a new user is approved from the moderation queue?

yeah after you install it you can just move its hook to register_addmember complete and I believe that will trigger it after the user has been approved if not Ill have to go look at it more in depth later

just streamlines it a little bit

#1 should install seamlessly over any old installations and should work perfect with those using a lot of mods and those using none

#2 is the same but wont overwrite your welcome message with a new one