>Both sound perfectly OK by me

Agreed Bingley. 'Have' has many uses - the ones I know follow:

It can act as a main verb:

1) She has a beautiful house.

or as a modal:

2) We have got to go back some time.

or a catenate (joining) verb:

3) One has to go to Paris to find decent clothes (grin)
or "I have to be home by four."

I don't really get all that 'auxiliary verb' crap you read about. I mean, a modal verb is an auxiliary verb - a modal auxiliary, right? The prescriptivist and descriptivist grammarians have a field day debating modal verbs, but I horribly under qualified for that. I'll stop there.

Aside: anyone know where 'to have a field day' comes from. A relic from the Great War?