QuickBooks does not have a demo version but they have an free online mini version which does not include all the capabilities but does give you an idea of the basics. To compare features of Pro vs. Online, check out
http://oe.quickbooks.com/compare.cfm.
I believe that you can get the basic knowledge from a textbook but like Gwynne said you really need to work in the program.
Don't forget to check online for free how to videos and tips. There are also some threads here on resources for both.