Overtones are easy, you can overblow an octave without too much effort, altissimo is a little more involved and not something I would worry too much about unless you really need to explore the outer reaches of the instrument.
Thanks for that help.
I've had a good look at Pete's site over the years and it's not altissimo I'm bothered about.I'm new to sax playing (Clarinet for five years then I got the bug!) and my teacher was showing me the overblowing with bottom Bb keyed.The secret I believe is 'the throat position' and try as I might I cannot get above the first.So I looked at the lessons here and did not find any help.
From a Pete to a Pete... Welcome to the BR I hope you find what your looking for. On another note (did you see what I did there ) isn't it strange how many liquorice stick converts we seem to get...just shows which instrument is best ;}