in maya you can make a skeleton ...... using ik ect..... the skeleton you would want to update to is the actual second life skeleton
http://wiki.secondlife.com/wiki/Mesh/Rigging_Fitted_Mesh
go to the download links in tab and download the zip.....
re rigg your clothing or attactment ... using that ... there are many tutorials on rigging and avastar is good to use if you use blender ..... I use maya..... but lot is the same between the two
you can rigg to a specific bind pose then convert it back if nessary ...... but your rigg should match up to the wieghts from the sl one collision will be 1.032, 0.98, 0.32 ((example)) mpelvis is the root all classic bones will be mpelvis mlowerback ect..... if you were doing fitted aka collision or liquid mesh you would be rigging and binding to collision bones PELVIS, BUTT, ....... ect
if your pose isnt in a t pose can set the pose and revert to tpose freeze transformation and delete history fix the minor stuff rebind and copy wieghts ...... there are many different things could do