Don't have to/need not

All I see is that (1) is less formal, Pieanne.

Is it the same for the questions?
1. Do I have to get up etc... ?
2. Need I get up etc... ?

For me, yes.

Thanks, Mr M. It sure helps clarify things when I have to teach that to my students.

I must admit, I do myself get a sense of 'internal necessity' (needn't) versus 'external necessity' (don't have to); though 'don't have to' seems to cover both:

1. You didn't need to do that.
2. You needn't have done that, you know.
3. You don't have to do that if you don't want to. Just say no.
4. You don't have to do that if you don't want to. No one's forcin

Could I answer as follows?
1. Yes I needed to take that money, for I've got to pay my wanadoo bill.
2. Gee, I did that to please you...
3. /4. Yes, I have to watch TV all night long, because tomorrow we're having a lesson on media language.

They seem OK to me, though the second answer doesn't seem to imply necessity either self-imposed or external.

Or maybe...

1.
A: '...Anyway, I just wanted to say: I'm very sorry. And just to show how sorry I am...' {produces expensive gift}
B: {small gasp} 'You didn't need to do that!...'

2.
A: '...Anyway, thank you very much for the loan. I've had it dry-cleaned...' {returns item}
B: 'Oh, you needn't have done that...'

3.
A: '...And at 5o/c, when e

Perhaps the song of the sluggard-- or AmE-- but I could still just as easily say either form in any of Mr P's lucid examples. And to me 'need' remains slightly more 'formal' ('BrE'?-- hmm) than 'have to'.

Sorry, MM, I should have said: to my mind, 'need not' has an air of 'internal necessity'; while 'don't have to' has an air mostly of 'external necessity', but can be used for both.

In the examples above, I would take 1, 2, and 4 as 'internal necessity', and 3 as 'external necessity'; which means that 'don't have to' should work in all the examples; but 'need to' only in 1, 2, and 4.