One way, to use older version of 3D MAX 4/5 and use the available export/import plugins and the conversion tools.
Unfortunatelly, for all those with Max v6.0 these plugins are useless since they’re not compatible.
Custom player model(s)?
Ikanatto has created a workaround for the player models:
http://www.splashdamage.com/index.php?name=pnPHPbb2&file=viewtopic&t=9593&highlight=
I assume that the tutorial is included in the following zip:
http://mak.s13.xrea.com/ET/archives.zip
Tried it, has great stuff and tools, but the most important plugins don’t work with 3ds max v6.0.
One quick question: from 1 to 10, whats the “pain-in-the-ass” estimate on modeling custom stuff for ET without the proper tools?
Just curious if it even is worth the effort and stress generated from trying. 
Sorry for any typos etc. and thanks in advance!
If you strongly wish to make some skins, it might be worth to try. I strongly did, so made a convertor to manage to do it.
However modeling itself is fun to see what you want in ET. The way how we export them to ET is hard without proper tools.
One quick question: from 1 to 10, whats the “pain-in-the-ass” estimate on modeling custom stuff for ET without the proper tools?
12 !!
As I said in the Player models doc thread, you can easily make MD3 map models because the tools are out there, but player models are a whole different matter.