Nope - not in any drives I know.
In fact I've only got one (maybe two - I seem to recall buying a DVD recently that was an DVD18), and that's a pressed, retail DVD, albeit a region 1 disk (T2 ultimate edition, one of the early, more rare pressings, later on it was done as two DVD9s).
I'm not aware of there being any data / burnable DVD18s yet - and given it took a long while for DL technology to filter through to the domestic market in terms of burners and media, I think it's a while off, if there's a need at all.
I don't recall seeing and double-sided burnables, but then I've never looked for them.
Set your booktype to DVD-ROM, use some blanks that are reliable for you - don't try to burn at too high speed at first - most burners go through something of a learning procedure with media.
Megabits (small b) ;-)
Given where he is (Australia, ain't it?) I think I'm with him - surely it would be easier to download?