When you say you "imported from an old D8 camcorder", do you mean you captured your video over a FireWire connection using Premiere Elements to control the capture?
Also, when you started your Premiere Elements project, did you select the settings for DV Widescreen?
Finally, if your DVD looks fine when played on your computer but looks 4:3 when played on a DVD player, it usually just means that the DVD is not triggering the player's widescreen toggle (which is very common with home-burned DVDs). What happens if you manually set your DVD player to play the disc in widescreen mode?
Welcome to the forum.
Along with Steve's comments and suggestions, back in PrE, go to the Project Panel (where you see all of your Clips), and Rt-click on one, choosing Interpret Footage and see exactly what it says about the footage. Does it show 16:9 with a PAR = 1.2 (for NTSC Widescreen), or 4:3 with a PAR - 0.9 (for NTSC Standard)? Note: PAL will be different, but you should still be able to tell if PrE is picking up the files' flag for Widescreen, or is seeing the footage as Standard.
Thanks for the suggestions .... hadn't thought of checking the settings on the DVD player (and to be honest hadn't thought there were any settings as you never come across them normally as relies on stopping a DVD then pressing menu) and found that it was defaulting to 4x3 mode. Switch that to 16:9 and looks ok - black bar on left and right gone - looks as if picture is marginally cropped on left as the "C" in "Created by Adobe Premiere Elements Trial version" is half off screen.
Had the DVD player for ~10 years and never had a problem with this before but assume that other discs (basically all pressed DVDs as opposed to DVD-R's) had the correct flag info to switch it to 16:9 but this didn't!