Naveen,
This error message shows, that you are not using OpenACS, where tdom is preloaded. To load tDOM in a decent configured tcl shell, use "package require tdom". If tcl does not find tdom, then either you tcl-path (variable "auto_path" in Tcl) is incorrect, or you have to install tdom. On systems like ubuntu/debian, you can use "apt-get install tdom". But of course, you can get the sources and compile yourself, but for a beginner i would recommend to focus on the task.
-gn
