Ah, I am using 2.5. I wasn't aware that 2.5 didn't work with rigged meshes. I'll try with 2.49b, thanks!
Well, the only way I know of how to explain this is through an image. I rigged a mesh in Blender to the SL skeleton. In Blender, the rig works perfectly - I can rotate every single joint and it looks just fine. I go to upload this rig into Second Life and... well... I've checked - repeatedly - for any errors in Blender but I really can't see what I did wrong. Could anyone help?