Well, after a bunch of reading and tinkering.. it seems that I can only append mass storage drivers via the screen in the first post, but I cannot change anything else about the syspep.inf that altiris uses when doing a create image job that has "Prepaired using Sysprep" set.
I'm rather surprised and disappointed that Altiris doesn't offer a way to change settings in the sysprep.inf, especially the OemPnpDriversPath, since DS 6.8 is supposed to be more integrated with sysprep than DS 6.5.
Well until I can, looks like I get to stick with:
-get machine ready to be uploaded
-get machine ready to be sysprep'ed
-take a snapshot with VMware

-sysprep & upload image before mini setup
-revert to snapshot after image is uploaded
Though if I'm wrong, please don't hesitate to say how I can do it.
Thanks again.