Can I learn to speak/write Quenya or Sindarin?
There is a great Quenya course by Helge Fauskanger at Ardalambion. Thorsten Renks Quenya and Sindarin courses and articles can be found at Parma Tyelpelassiva. Another good resource is the Plaza house Tham Lammath Edhellin. Some of Taras Sindarin grammar lessons and helpful tools are available on the Rivendell kingdom pages. Ryszard Derdzinski has some articles at Gwaith i-Phethdain.