To be honest, if you can pass the 70-461 Exam by August 1 after knowing nothing about on July 1 then you should be your boss's boss.
Still, it is worth perusing to see if that is the direction you want to take your career. If you're like me just reading a book won't cut it. I find it easier if I can get my hands on it. Here's a low-cost way to get started:
As others have pointed out, you can download SQL Server Express With Advanced Services for free. I'd get the 2014 version but if you don't have at least Windows 7 SP1 you can get the 2012 version (which works on Vista).
Next, go to codeplex.com and download the AdventureWorks2012 sample database.
Use the documentation or Google as a source to install SQL Express, and then install the AdventureWorks2012 database.
Now see if you can figure out how to get a list of all the names in the database with a specific last name.
Next, read about JOINS and get a list of the same people and their addresses.
If you get this far, you'll be started on your way to being ready for the 70-461 Exam. Since this exam is about queries I believe most of the skills you need can be practiced with the free Express Edition.
Also study how to backup & restore databases, then practice it. This is a vital skill to have, especially when you start to practice modifying the database you'll probably mess it up and want to restore it to what you had before.