Rigging MC to the UT3 Male skeleton...

[t3h m00kz]

Whats the deal with custom rigs again?

You can either:

1. Size a model to the existing skeletons and have it use the base animations, or
2. Create your own model with your own skeleton and make an animation set specifically for that model.

[itszutak]

Are the default halo animations formatted in such a way as to make conversion ridiculously difficult? (I imagine so)

[neuro]

totally different animation system, you'd only be able to use about half the animations.

[t3h m00kz]

UT3, if I remember correctly, uses 125 animations per biped skeleton. Not exactly something one could get done in a day... at least not without some pro skills.