Ok,

after various posts and replies from others (thanks all) and a lot of messing around (and blank DVDs used) I've finally managed to re-encode a widescreen SVCD to DVD using ISOBUSTER, TMPGEnc+ and TMPG DVD Author as follows:

1) Rip MPG2 file(s) using Isobuster
2) Join files if necessary using TMPGEnc+
3) Start new project in TMPGEnc+, choose DVD (16:9) template, source aspect 4:3, output aspect 16:9, Video Arrange Method - No Border, Maintain Aspect ratio
4) Set the bit rates, press go and go to bed
5) Import into TMPGEnc DVD Author
6) Burn disc with TMPGEnc DVD Author
7) Play in standalone DVD player with a smug grin

Hope this helps people out,

Jukka

@Baldrick - If I write a guide for this how do I submit it?