Anybody knows if Ulead DVD Workshop can author DVD's in 16÷9 format? And does it support the PanScan function?

The answer is NO.
You must to use the DVD Maestro to enable 16x9 with PAN-SCAN feature.

And what about Sonic Scenarist?

Very few fully support 16:9 but you can fix any program out put even if its 4:3 so that it will do the right thing.

The program infoEdit is used to re command the inf files to auto letterbox or what ever you need in the outcome. The same program will fix the pan & Scan thing that has been asked here.

Till Maestro I used SpruceUp for 16:9 the process to use it was first posted whilst I was away in New Zealand. Here are the URL's

Mine:

http://geocities.com/xaussie01au/DVD_remote.html

that leads to Gareth's how to do it in dtail as there was no point in re-inventing the wheel or repeating the info on my page:

http://www.ghorne.pwp.blueyonder.co.uk/vidtest/169frame.htm

The only thing infoEdit will not change is to use 4:3 and 16:9 menus in the same project. DVDMaestro obviously codes another area that infoEdit does not access to achieve 16:9 menus and 4:3 menus on the same DVD disk or at least I have no skills to do so.

Be aware also as pointed out on my web site page the menu selection patches probably will not be correctly positioned in the letterboxed case when a 4:3 authoring program is tricked into doing 16:9 thats why at that time I designed the funny looking menus you see on my original web page. A means to an end.

The Tutorial from Garret's seems not to work on my case.
I used DVD Workshop for authoring, and after creating the DVD folders I used IfoEdit to do the trick.
I burned those folders with Nero... and I got a video that is streched up in a 4:3 television set.