I am going to be taking my C2 this fall.. so I have not yet taken an HB, but I have studied HB for Quiz. That's a lot to take at one time, because the C2 is a long test that consists of you jumping three-foot, having an up to date record book for nine months as well as a conditionings schedule. There's also about 2-3 pages of knowledge and information you have to study for. http://covered.ponyclub.org/C-2Testsheet2009.pdf
Heres a link for the test sheet with everything you need to know and perform at your C2 testing.
For your HB... it is ALL information. NO riding. So you need to study study study all of your manuals. Especially the A/B and C Manual. There is LOTS of information that will be on the HB test, and remember... you need to make sure you can recite all of it before you get there. After studying, have someone read off this test sheet here> http://covered.ponyclub.org/C-2Testsheet2009.pdf
And practice reciting and demonstrating your answers on your on pony/horse. Practicing always helps for before you get there.
For your HB you also have to be able to teach an unmounted lesson... so prepare for that ahead of time and go ahead and try and have a few at your barn. You also have to have 6 hrs of mounted lesson assistance... so ask your instructor if you can assist her for pony club. Make sure you practice your safety checks as well, and have someone next to you with a Safety Check sheet that they use at Rally, to help you remember how everything fits and why it fits that way. Your DC also has to sign off, saying that you did your 6 hours of assistance. Bring that along with your other stuff to the testing.
I think it's smart that you are already starting to study! :) Good Luck!! You'll do great!