Short answer, fall of 2007 and beyond.
Long answer- according to Steve Sansweet, head of Lucasfilm fan relations, a Star Wars 3D animated series set between the Episode II and Episode III- during the clone wars- is in pre-production as of February 2006. It is slated for release in the fall of 2006 and George Lucas is remaining involved with the entire process.
A live action series of “100 one hour episodes” (according to Rick McCallum) will not get under way until later and may not hit television screens until the end of the decade- i.e. 2010. This will be set between Episode III and Episode IV.
The series are not based on any of the main characters. Contrary to rumors, Clerks director Kevin Smith is not involved (as of February 2006).
(Some information courtesy MovieWeb)