For right now you can load them into Sandbox using the obj file included in the downloaded models.
Follow this tutorial:
viewtopic.php?f=24&t=293
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Updates on the tutorial since written:
Now we have a my_stuff folder so you do not have to put your new folder under the packages default folder anymore
You do not need to change image files to a jpg files, just rename the auvBG.png to skin.png as the tutorial describes in changing names.
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Also you can add these lines to the obj.cfg file.
mdlspec 40 That controls how shiny or dull your mapmodel is. Lower numbers = duller in appearance... so 40 has some shine to it.
mdlscale 1000 That controls how large your model is. Higher number the larger in size your mapmodel. 1000 would be well, fairly large.
Open up the obj's mtl file and remove this line:
map_Kd auvBG.pcx (Remember each model will have it's own map_kd line in it.) Whether this line needs to be remove or not I did not test to find out but it's pointing to a file format that Sandbox does not support.
It will not affect the correct loading of your mapmodel.
Edit:
I posted a picture of my folder pilaar with the files so you can see them.
I also just converted the obj to a md3 after but the above will get ya'll going. later this weekend will update the post to include the coversion to md3 files.
I believe the license allows you do this kind of modication but read them to be sure...