I have a Skinned Model, I have got it animating just the way I want it but thought it might be a good idea to model the BoundingShere's I want for collision inside XSI. This way I will be dealing with something I can visualise. I can see how I can pull out the details of various meshes but when I can't see how, within XSI I can animate various meshes.

I have added the spheres in XSI and can animate them within the program, I can also see the variuos meshes within XNA, however when rendered on screen in XNA the models look like they are just the default size and position (Radius: 4, Center: 0,0,0). Whenever I look in XNA at the values of the BoundingSpheres the Radii seem to be fine, but don't look fine, and the centers sit at {X:-1.527227E-07 Y:-3.876191E-08 Z:4.214683E-08} and don't move.

I have tried adding the meshes to the character key set, which I never thought would work and didn't. Is there an easy way to have multiple meshes animated within one XSI file?

I have been going bonkers trying to figure this out and have had another thought. Is it easy to add tags in XSI, I can see you can add tags to a rig, which I have tried, but the Tags element of ModelMesh contains a null.

What would be the best and easiest way to set positions for BoundingSpheres for collision on an animated SkinnedModel with a single Mesh?

A few things...

I am not sure you can combine mesh matrix animation with bones animation in XNA (I may be wrongly assuming). The only thing I can think of is that you could create a parallel model hierarchy (as a distinct model asset) that will contain your bounding spheres and their animation.

For the second option you are mentioning, there are currently no custom data pipeline between Modtool and XNA, although you could possibly write a script that writes up an XML file that contain that extra information (i.e. the bounding spheres properties and the bones they are related to). You can also refer to the code of the XNA integration plugin to see how you can automate it (just look in the plugin manager where you can find and edit it).