What OS are you using? I'm not sure if that stuff is still working under NT (Win 2000 or higher). Than you have to link it directly to an exe (with Link) and execute it.
If so than have a look at the BIOS-interrupt INT 13h ( http://www.ctyme.com/rbrown.htm - bookmark this site it's very, very, very important and Ralf Brown is your God!). Int 13h can also be used in the oder DOS-Versions so you bet use that in the future.
By the way: I also startet with Jeff Duntemans Book "Assenbly Language Step by Step" and I can guarantee you that this book is one of the best to start assembling. So keep going!
Greetings
Simon
PS I think that INT13h is also covered in that book a few chapters a head. Have a look there.