That is depend on TinyMCE (wordpress internal text editor) plugins. You can install "Advanced WYSIWYG Editor" http://www.labnotes.org and modify the code.
function extended_editor_mce_buttons_2($buttons) {
// Add buttons on the second toolbar line
return array("separator",
"cut", "copy", "paste", "pasteword", "undo", "redo", "separator",
"table", "sub", "sup", "forecolor", "backcolor", "charmap", "separator",
"spellchecker", "code", "fullscreen", "separator", "wp_more", "wp_help" );
}
The key is "pasteword".
If you wanted to paste MS Word table, you must install TinyMCE table plugin. If not, the table will truncated.
Sorry, bad english.