half.com is a good site.
but half.com was purchased by ebay.com and will be shut down in 10/2004.
ebay.com is supposed to take all half.com's feature and provide similiar service.

旧书 还有 alibris.com 等等.
很多书的international edition 相对便宜，我在这个英国网站买过一些新书，不过shipping 较慢。
http://www.whsmith.co.uk/

btw, 这里有个很强的search engine 可以搜书价。
http://www.addall.com/

It depends. If most of the exercises/assignments will come from the textbook, better buy the EXACT edition mentioned in the syllabus. The case/exercise numbers may change with each edition. I've seen students turn in wrong assignments because of using older editions. The savings don't worth the hassle, really.

那有没有JJ知道我第二个问题呀？

如果价格相差不多就买最新年份的咯~ 如果价格有一定差异还是买便宜的,始终还是一个版本不会很大出入的. 我经常是买低一个版本的呢 :P

有两种可能:
1. 一本是hardcover, 另一本是softcover;
2. 这两本书是不同的出版商出的.
如果是这样的情况, 只要版本号是一样的, 内容就一样.

i usually use www.addall.com.
but it doesn't include information from www.walmart.com and some other UK websites. For these, i will check out walmart.com and google the bookname from UK websites.

图书馆借呗，馆际互借，全美国的图书馆的书都能借。我来美国从来没买过一本书