Some questions about the hkt file,xml file and the hkx file include?

Accroding to study the Havok_Physics_Animation_2012-2-0_Pc_Xs_User_Guide,I have some questions:

1、I get to know there are three 3D format files can be load into havok.They are  hkt file,hkx file and xml file.But now I want to know what differences between these 3D format files? what information they include? 

2、if I want to load other 3D format files such as .3ds and .ply  into the havok,what should I do? Who have codes and metheds can load these 3D format files into the havok and wanna to share it to me?

I know there are many predecessors,so I want to get your help. thx!

                                                                                                                                                                                                                            Wang L