I wouldn't sweat it. Soft 3D is a very mature product that gets the job done well. The transition to XSI only has to happen when you are ready. If you already know Soft3D, then XSI is a natural progression to your existing skills.
Bottom, line...learn to animate first, and worry about these other issues later. 3D Software will always be changing, so there is no avoiding it anyway.
Hope this helps,
Urp