I'm not quite sure what you're asking, but I'll address the most common concerns.

Every object in a 3D space has a "center." With the rigs that Poser users, the relative center is going to rest with the "hip" of a human figure.

When you are exporting a human figure, for use in altering in a 3D app so that it can still use the same base rigging in Poser, the figure must be exported with all of the rig's "joints" at their default position, which is always with all rotations being "zero."

What this means is that the figure's hip must show 0.00 x, 0.00 y and 0.00 z. The figure's various joints must also be at zero rotation, which would be, generically, 0.00 x rotation (Typically "bend"), 0.00 y rotation (typically "rotate") and 0.00 z rotation (typically "side-to-side" or another "bend").

In Poser it is easy to do this. Simply "zero" the figure. In PoserPro 2012, one would open the Joint Editor, select the figure, preferably the Hip of the figure, then click the "Zero Rotations" to zero all the joint rotations. Then, check the hip to be sure it is reading at 0,0,0 and the Body of the figure, to be sure it is as 0,0,0 as well.

One thing to be aware of is "scale." If there are any scales currently being used in the figure, they should be at 0% when the geometry is exported. If you intend to use scale in the figure, once your changes are imported back into Poser as a morph or as clothing for scaled figure, you should leave that for adjustment in Poser. IOW - Do not export the geometries/rigging of figures/groups/rigging that have been rescaled from their default sizes.

May default Poser figures do not have their feet resting exactly on the "ground" plane. That's fine and it means nothing. The only thing that is important is that the figure is fully zero'd relative to position, joint rotations and scale when the geometry/rigging is exported.

What has likely happened is that the figure was not exported correctly from Poser and/or not imported correctly or kept stationary and locked into their position in your 3D app. Pay special attention to import/export choices that could change the important position/rotation/scale properties to be different from the default figure's.

There are tutorials out there for clothing creation for Poser. Do some searches for clothing creation and import/export requirements and you should find some tutorials and videos that will give you all the basic information you need, including export options/import options and rigging.

(IF I had the figure, I could give more precise instructions, but I know nothing about the figure or your version of Poser, sorry. IIRC, Cheetah 3D is a Mac 3D program, but there shouldn't be any substantive problems, there, as long as your import options do not make changes to position/rotation/scale of the figure as it was exported from Poser.)