Thanks TurboPT for offering your help. I think I can not make a sandbox available to you because of very strict security rule in our company. But I will update you and others of the progress as I have been looking into this integration and asking for any hint for a while, but no reply. So, I definitely share with others my experience and solution.
Regarding your question about command-line, I'm not using any command-line equivalent. Generally speaking, I've written a small piece of program in C# and using Microsoft API to connect to TFS. In the same program I've made a couple call to APIs for reading the data of a desired defect number. In next step, I call that piece of code, which is in C#, from Testlink, which is in PHP.
What I've explained above is simply the high level design. Although it looks simple and easy but figuring out what to do took me some time. With this simple procedure, somebody with a little bit programming experience can implement it. However, I'll provide all details and code in this forum. I prefer to get rid of some issues that I've mentioned in my previous post, then take care of documenting and provide you with all details.
I've uploaded 4 images to imageshack that shows how a bug in TFS is added to testlink, Let me know, if you can't access to following url, as this is the first time that I use imageshack:http://imageshack.us/g/854/addingtfsbug91948totest.jpg/