oh man, thank you guys soooo much.
just so it's here in case someone else needs it:
(setq prefs(vla-get-preferences (vlax-get-acad-object))
filePrefs (vla-get-files prefs)
)
(vla-put-PrinterConfigPath filePrefs "c:\\path\\path")
(vla-refreshplotdeviceinfo
(vla-get-activelayout
(vla-get-activedocument
(vlax-get-acad-object))))
(setq prefs nil)
(setq fileprefs nil)