There doesn't seem to be any "Powered by Mac OS X" badge anymore, but I believe you can use the "made on a Mac" and "Powered by Darwin", or the "Powered by Mac OS X Server" one if you're using it.
The font is some Myriad variant. Probably Myriad Pro.
Toast, I believe, put a link up somewhere to a site that would identify fonts for you, provided they are large and clear enough, from an uploaded picture. If I find it, I'll post it.