If you want an introduction ebook, try Assembly Language Step by Step. It's published in 1992, so it's pretty new (for assembly), and it starts very basic, including how to count to hex and binary.

I may say it could be more useful than the Art of Assembly since this is directed as assembler proper (if I recall, doesn't Art of Assembly focus on HLA?).

Anyway, you can get it at the runnet site: fxp://ftp.runnet.ru/BOOKS/, file name is ASSEMBLY_LANGUAGE__STEP_BY_.ZIP, just 6.4Mbs.