hi,medsport! you cite the author of the quote and use the information from the references section of that chapter for your bibliography information. don't mention the name of your textbook as being the source of the quote because the textbook authors are not the authors of the quote. if you really want to be "pure" about it, find the original reference source. what you'll find, however, is that the textbook authors quoted it directly from that reference, or they should have. i have found quotes like this before and gone to their original source and found the authors had cited the quote exactly from the original source as they were supposed to and given credit as they were supposed to.
as far as how to present it, textwise, do whatever your mla rules say. doesn't it have to take up a certain number of lines before you can indent it and set it off from the rest of the text of your paper? it's been a long time since i've done mla style, so i don't remember all the rules. does your college have an english lab where you can go in and have someone look over your paper for correctness of grammer and style for free to help you on this point?
by the way, when you are getting ready to do your bibliography, or works cited page, you might want to use landmarks citation machine here: http://citationmachine.net/
all you have to do is input the information it asks for and it will format it for you. all you have to do is cut and paste the formatted information it spits back at you. i found this site a couple of years ago when i was working on a paper and looking for apa rules and since then the site has grown. this service is free and they are able to format in mla and apa styles. according to their site, they are currently working on getting turabian rules into the software. using this site will take a lot of the headache out of setting up your bibliography entries.