Kari,
all PAL-DVD-players could play NTSC-DVDs, so 23.98 would not be a problem, but you need to set your video as 23.98 not 24fps.
be awared that PAL has 720×576 and NTSC has 720x480px, that´s a bit less.
be awared that SD DVDs feel like eye-cancer if you only have seen the high res-files.
so you need to set your premiere-output (and/or the tiff-sequenz) to 23.98 to have a propper SD NTSC-DVD-workflow.
don´t sent your premiere-sequenz directly to encore, just export it to your harddrive as selfcontained movie (AVID DNX HD AVI or quicktime PRO RES, depending if you are on mac or pc) and encode it to NTSC-MPEG2 using adobe media encoder and a self-created preset with 23.98.
media encoder will create a 29.98-file out of it with the necessary pulldown, as DVD could only be 25 or 29.98, depending on your TV-system (PAL or NTSC).
use this file for authoring and set your DVD-project to NTSC.
cheers
danny