if you need a textbook quick i recommend textbookexchange.com. upside, you get the book much cheaper than the co-op (as it's second hand they're usually around half price), but the downside is that you need to organise to meet with the person (unless there's a postage option).
i got mine heaps cheaper i.e. eco from $118 to $55, mgmt from $90 to $45 and accounting from $134 to $80. i emailed people about the texts i wanted on saturday, by monday i had two and i'm getting another on weds.