This has been answered 20 million times before.
It starts "06"
I don't think I've ever used my personal ID before FYI. It's hardly critical (although you should keep it secure).
I always include my Personal ID when I'm e-mailing universities. Dunno why its required though... I mean our application number is unique isn't it!
your application number should start with "06", and has 9 digits
your personal ID has 10 digits (well, at least mine does)
no they're different things. your application numbers printed on your offer letters and your letters from ucas confirming that your in the system.