The following diagrams provide an understanding of the structure of the various ITIL V3 qualifications and the associated 'credit' scheme recognising the value of ITIL V1 and ITIL v2 qualifications.
Details regarding the ITIL v3 courses can be found by clicking here.
ITIL qualifications Scheme Structure
The 'credits' documented in the above diagram may be subject to change as the ITIL V3 qualifications scheme is still subject to approval from the ITIL V3 qualifications Board.
See also - this article.