You can post whatever you want in Tamil. Just go through the thread
http://www.chennaispider.com/forum/68-Write-tamil.aspx in the forums.
But before you post be sure that it is not taken from the copyrighted pages of the net. You can send a message to our webmaster Rajmi Arun and find out in details. She will tell you what to do.
Always add a summary / meaning of the shloka or the poem you are adding, in English also. Not many would be knowing to read Tamil, so an english summary will be easy for them to uinderstand what is going on here.