Basically there are two sections;
The beach itself and the grass verge which runs along side the beach,
The beach hosts the main stage and the 30,000 strong crowd, if you are towards the back of there you probably have little to no chance of meeting anyone famous, although there are plenty of famous people to see (on the stage) lol...
If you wonder around the grass verge (the fairground, bar areas etc) you may be lucky enough to catch glimpse of the mentioned, eastenders, shepwrecked, big brother, hollyoaks cast members.
Any acts that actually are performing usually stay in the backstage area of which, unless you've won competitions etc the public do not have access to.
Hope this answers your questions,
Jack
T4 On The Beach - 20th July 2008 - Weston-Super-Mare