This is the link where you can download the SDM without need to register an account at CISCO. Although registering the account doesn't cost any money , but still feel annoying while try to get the SDM fast and immediately. So here is the link , which you can click and download without any question.
If you need a guide on how to install SDM , here is a good guide.
Hope this two page will help you to setup the Cisco SDM at your desktop.
Another tips before I forget , if you connect to the device using ssh tunnel, most of the time you will access localhost , remember to use localhost instead of 127.0.0.1 , using ip address will cause the SDM failed to launch.