Just letting folks now, I've made an update to my 3DS Max 9/2008 SMD Export plug-in.
I've added support for HL1 format SMDs and a crude but functional batch-mode which you can call from Maxscript. I've also fixed an irritating bug with Export Selected not working if you only want to export part of a bone chain and don't include its root/parent bone.
SMD Importer is still WIP but no ETA as it's very much a freetime project of which I don't have much of.