Hi,
1.The Sdm tool is available free on all routers , Cisco 830 Series to Cisco 7301. It shipped preinstalled .ASDM you may need to install as per your ASA/Pix ios .
2.Asdm is security management and monitoring services for Cisco PIX 500 and ASA 5500 series adaptive security appliances through , web-based management interface .
Asdm can be used in case you are running version 7.0 and above.
3.Cisco Asdm you can download from the software download page with a valid contract cisco user id :
http://www.cisco.com/cgi-bin/tablebuild.pl/asa
http://www.cisco.com/cgi-bin/tablebuild.pl/pix
4.It is a user friendly GUI config tool .
Please follow this link for more information
http://www.cisco.com/univercd/cc/td/doc/product/netsec/secmgmt/asdm/v_5_2/rn522.htm#wp65945
Raj