Seperating Joined parts on a mesh in blender

Hi im new here and hope im not posting in the wrong part of the forum. Ive actually been using XPS for the past 6 months and have just started to take a stab at using blender 2.49b recently. Ive got the hang of its basic features so far but I would like to know how do you separate joined parts on a model using blender? Heres whats going on, I want to combine one models torso with another models legs in XPS . There is a tutorial on how to do that on deviantart. Anyways, the problem is, on one of the models im using, when I attempt to disable her shoes in XPS's "Make Items Optional" feature, it disables her shirt as well. So I cant disable the shoes by themselves without it also disabling the shirt. Does this make sense what im trying to say? I guess the person who originally converted the model either accidentally joined the parts together or forgot to separate them. Can they be seperated in blender? Thank you

Im using the latest version of XPS by the way if it matters ((XPS 10.9.3))

Right, for this issue you need Blender.

Video made by our administrator: [You must be registered and logged in to see this link.]
with russian, and english subtitles

Written original tutorial with my poor english: [You must be registered and logged in to see this link.]
Perfect english traslation on DeviantArt [You must be registered and logged in to see this link.] -- But dont use "XPS-->File-->export selected as .mesh.ascii" -- Use always "XPS-->Modify-->Save_Generic==>.mesh.ascii" (Shortcut F11)