In essence, we're working on it :)
It's just a question of timing, with release candidates and when the first service pack is released ;) We've done preliminary tests and we've found similar results to what others have found. We know we have to do more comprehensive testing with all the flavours of Windows 7 as well. As well as continuing to support XP and Vista as well.
Currently we're uncertain how immediate the update of installers will be after release of Windows 7 but it will be done.
Let's not forget that we'll be adding lots of games to GOG.com (lots of great things in the pipeline:))) whilst having to update existing games.
You asked about the 64-bit support -- we release games on GOG that we have done compatibility magic/tested on XP (32 & 64 bit) and the same goes for Vista (32 & 64 bit). We tend to have to do Vista compatibility magic to get some of the games to work on Vista eg. Silent Hunter 2 which when released will be Vista (32 & 64 bit) compatible.

AFAIK game publishers would have to register games with Microsoft to have it appear "normally" in the game explorer. I would have to check this with a programmer but I think we add our own large logo to the games explorer with some info/functionality.

Yes, you're mostly right :)
Currently we're changing our installers to show properly under Games Explorer. It will take some time to upload and rebuild all our games, but eventually it will happen :)
As far as I know, all games released after 10th of June should appear in Game explorer w/o problems.
Best
Grah