I believe that the test CD is the same one you would get in the Arco book sold in bookstores. Actually, the CD that comes with the Arco book has some extra tutoring material (little 20 minute tutorials on various topics). Plus you get a book. The Manhattan CD is simply the test part licensed over to Manhattan and released under their label.
You can get a used Arco book w/ CD for less than $10 on Amazon.
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993