http://anon:anon@macromates.com/svn/Bundles/trunk/Bundles/ Experimental HTML.tmbundle, I suppose.
oh, blast, didn't see that one. Sorry :(
So the exact instructions to get a local copy, if you already have svn:
cd ~/Library/Application\ Support/TextMate/Bundles svn co --username anon --password anon 'http://macromates.com/svn/ Bundles/trunk/Bundles/Experimental HTML.tmbundle'
Then restart TM and there's a new Experimental HTML bundle with the grammar.
When you want to update it (since it's work in progress), do:
svn up ~/Library/Application\ Support/TextMate/Bundles/Experimental \ HTML.tmbundle
Or just copy/paste from the webpage? In any case, that seems to be really cool stuff and when it's ready and taken advantage of by some good themes, TextMate should begin to shine quite proudly amongst web editors (even more so than now hehe)
Andreas