Quote - I've got a some more information on what is happening when I use a single scene file.  I'm still not exactly sure "why" it's doing what it's doing, but here's the process I'm using.  If it helps, this is also running on a 64-bit Windows Vista installation, with wxPython 2.8 installed.  I get the same results whether or not I select the option to use the Poser materials on import.

1.  Import the scene file, selecting "Group Figures as single meshes"
2.  Rename each 'body' object as noted in prior post

If I look in the material editor, I start out with 84 materials, with separate materials for Mike and Vicky, but each figure has the same material names.  For example:  2_SkinHead, 1_SkinFace, etc. 

A-Okay so far

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3.  Select Mike, Load SkinVue, click Select and then Swap

At this point if I look in the material editor, if I click on Mike I now have 52 materials, with a Michael4_Body_E, Michael4_Limbs_E, etc with M4's maps, But now all the 2_SkinHead, 1_SkinFace, etc maps for Vicky are gone from Mike's materials list.

This is normal.  The old Poser mats for Mike (e.g. 2_SkinHead) will be exchanged for SkinVue mats (e.g. Michael4_Head_E)

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But if I click on Vicky, it displays 84 materials again (??), with all of the original 2_SkinHead, 1_SkinFace, etc, listed for both Mike and Vicky.

What do you mean by "for both Mike and Vicky"?  In your step 3 above you indicated that the old Poser materials for Michael 4 were gone -- replaced by SkinVue materials.  The only materials which should be highlighted in the WorldBrowser Material tab for Vicky should be only for Vicky.  There should now only be one 2_SkinHead material for example.

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4.  Select Vicky, load SkinVue, click Select and then Swap. 

If I look in the material editor now, I still have 52 materials listed when I click on both Mike and Vicky.

If I select Mike, I have Mike_Body_E, etc, with Mike's maps.

If I select Vicky, I have Vicky_Body_E, etc ... with Mike's maps.

This is bizzare.  I just ran exactly the same test with an M4 and V4 character combined in a single Poser file and it worked perfectly - M4 had all of its maps and V4 had all of its maps.  What version of Vue are you using?  I'm on Vue7 Infinite build 39290 with XP64.  I'm wondering if there is something strange about your Poser file that could be causing some type of cross-talk.