Anand,
I don't know if you know about the search field in the upper right hand area of this discussion page. It works great for searching on topics.
I see that you have posted three times about top down assemblies. I was going to link you to a conversation, when I saw that it was started by yourself. If you need an update on a post, you can go ahead and ask further questions on the same post. This will keep the string of logic together for those who may have questions in the future.
For some multiple users, check this link out:
http://communities.ptc.com/message/201428#201428
Thanks, Dale