Grafting is a practical art that is best learned firsthand from someone with experience. There are some links in our
http://www.bonsaitalk.com/links under Techniques->Propagation->Grafting. There's a link to Colin Lewis's
thread graft discussion, at the bottom of the linked page, which is a nice introduction to this particular type of grafting.
Unfortunately, grafting is so technique dependent that it's a little like dentistry - you could learn it from a book but I wouldn't be volunteering to be your first patient.
The available books are really geared toward propagation of fruiting and flowering plants, not so much towards aesthetics, which are important for bonsai.
As to when, usually you want the understock to be active and the scion (grafted on part) to be dormant. So, grafters often promote extended dormancy in the scion stock by either keeping the plant in the shade, cooler area, or collecting scion wood and storing it in the refrigerator until the understock starts to come out of dormancy.
P.S. What are the seeds for?
Regards,
Matt