What if I want to build a device to run Android?

I'm really interested in slate tablet style computers and I'm looking into building a prototype of one this summer. I think it would be cool if it could run Android and leverage all of the apps people are writing for that but I can't find any info about what hardware to use. Can someone in a garage build an Android capable device? Is it really an "Open Handset Alliance" if the only people who can build the handsets are established phone makers?

Anyone have any info on this?