Indeed you need adminstrator rights to use Workbench. But in 4.2 version, you should be able to use it with normal user rights.
Below is the link to Workbench Installation Guide v4.1:
page 4 System Requirements and Prerequisites
Below is the link to the TM ART v4.1- Release Notes, Technical Bulletins, and Manuals:
As stated by others 4.1 does require admin rights, and 4.2 does not.
however you will need admin right to install 4.2.
once installed admin is not needed to run the application.