How can i create a cloud effect?

Hi, there are several ways to do it, the most simple are billboarded textured quads. If you want a more complex effect, check out the following links:

http://freespace.virgin.net/hugo.elias/models/m_clouds.htm
http://www.bartoszewicz.neostrada.pl/clouds/generated/generated.html
http://dynamo.ecn.purdue.edu/~ebertd/nvidia/PURPL_results.html
http://www.cs.unc.edu/~harrism/clouds/index.html
http://www.cs.utah.edu/~jmk/simian/

you forgot about GREAT thread on graphic theory forums:

http://www.gamedev.net/community/forums/topic.asp?topic_id=86024

You should never let your fears become the boundaries of your dreams.