Scanning and posting the book would be illegal, as would copying it in any form.
I've never tried register's book, but I can also vouch for Danny Goodman's HyperCard books. Also, if you're in the market for books, this seems to be the time of year (at least in Pittsburgh) when everyone is having used book sales. I've picked up a bunch of thick Mac books of all ages for only a quarter at these sales in the past. Even if you don't really find any good Mac books, you can get plenty of other good stuff for next to nothing.
As a sidenote, you won't find old Mac books at Half Price Books or a similar store. You may be able to find a book on OS 9 or AppleWorks 5, but not System 7 or HyperCard. A lot of the computer books here seem to be old stock from bookstores that they either couldn't sell or had to give up due to going out of business (a sad trend among small bookstores). Some of them are new, as is some of the discounted software you may find there, but again, the software selection is sure to disappoint--most of it is for Windows and is the half-rate commercial software sold to novice users.