I used to work for waterstones until last month, so here goes....
Working for waterstones is great, if you can get in!! It's difficult to get a job because so many people want to work for them, in term time we used to get 2/3 people a day asking about vacancies/handing in cvs and thats when we weren't even advertising! The best way, undoubtedly to get a job is to apply for a xmas temp job. Christmas is the biggest intake of new staff and you stand a much better chance if you apply at christmas. Waterstones are very picky about who they employ so if you haven't got any previous retail or (indeally bookselling experience) xmas is best. Most branches are fairly flexible about hours, even during term time. They employ lots of students, so the best thing is to ask at your local branch and keep your eyes peeled for any ads in the windows (they're normally only up for a few days), it's also worth downloading the application form from the website and handing that in anyway.
Hope this helps, any other questions let me know
kat1311