The instructor-led training for Cisco's network management products has always been a bit lacking. The last I heard there was a formal partner-led training class due out this summer. There is no specialization certification that I am aware of for Prime (or other Cisco management offerings).
You can refer to the nice series of videos on demand that Cisco has published on Youtube:
http://www.youtube.com/watch?v=sFrPLfykj6Y
They are up to about 17 segments in that series now.
You can also of course refer to the documentation on the product support page. There are also a couple of good whitepapers on the product information area.