Al-uh-STUR will do you if you're not in Scotland. If you were in Scotland you'd never have to ask - spit in any direction and you'll likely hit either an Alistair or an Ian/Iain. Out of 30 computer consultants I managed in London, 2 were Alistair's - Big Al and Al as we called them....Big Al was in management, Al was one of the 'young ones'.
You know how to say Kevin McCallister? McCallister is what happens to Alastair/Alistair/Alasdair's son in Scotland - take off the McC bit and you'll be on the right path.