BUSL250, not a very good textbook but u will definitely need it cuz the mid-term exam (half failed) is an open book one.
ACCG200, yes u will need it if u wanna get a D or above.
ACCG250, totally rubbish but if u wanna get high grade and have the ultimate patience to read the book, u should buy the book.
ACCG253, I have seen no one passing it without the book.
I have all the 4 books, if u're interested just send me an email. But, to tell the truth, I knew that the summer school used another textbook 4 BUSL250 (mine was only used 4 the 2nd semester of 2009 however) so they may change the textbook again next semester (so 3 books 4 3 consecutive semesters, what an INSANE). Wait until ur lecturer in charge confirm it. And the ACCG250/251 one has been used for more than 3 years so they may also change it?