Are you talking about outputting H.264 mp4 on a DVD disc? That's possible. But I don't think it's what you're looking for.
If you're talking about outputting a hi-def or BluRay video file onto a DVD disc, you can't do it in Premiere Elements.
I'm aware that it can't in PE but am looking for a progamme into which I
can export the finished, edited, file to then play back in HD in a
Blue-Ray player but from a DVD. I've seen it done using Toast.
Both Magixmovie edit 16plus and sonyvegas can do this .I do it in Pe 8 using a virtual burner Pe 8 sees a bluray burner and go fro there .its not free but cheaper than those programmes and the trial is unlimited other than only allowing 1 and a half gigs . Here is the link its very straight forward http://www.elementsvillage.com/forums/showthread.php?t=55009
That may be where the confusion is starting, Geoff. You're using "AVCHD" interchangeably with "BluRay" video files -- and they're very different things!
Are you looking to put BluRay files on a DVD? A number of programs, including DVD Architect Studio 5, can do this.
But AVCHD on a DVD? That's something very different.