sbaywatch,
I started my PPL this summer, thinking that I'd get it all completed in my 6-week holiday, (I am a teacher). However, I didn't complete it, and am currently up to the cross-country stage. And so, to offer my limited advise, I would get those lessons booked ASAP. Yes - lots will be cancelled, Yes- you will get pissed off. But at least you can begin.
I just wish that I had started earlier, because then I might have actually passed my licence. But as other posters have rightly pointed out, you do get used to having lessons cancelled. Just to put you more in the picture; in the summer, I had 4 hours booked every day for 2-weeks, and I actually only flew for 2.1 hours in total. So don't rely on good weather in the spring and summer...we're in England for F**K's sake !
P.S I've sent you a private message! (Not as dodgy as it sounds...honest!)