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Android is OpenSourced, and you can build it yourself on MacOSX or an Ubuntu machine. THis is not the emulator, but real Android OS running on your system.
http://source.android.com/download
Has the directions.
Check out the known-issues page before giving up- there are some rough edges.
10/22 Update: watch out for your file system on the mac, you need to have one that is paritioned and formatted with case sensitivity, I just found out:
~/work/mydroid [558]$ make build/core/product_config.mk:229: WARNING: adding test OTA key build/core/main.mk:58: ************************************************************ build/core/main.mk:59: You are building on a case-insensitive filesystem. build/core/main.mk:60: Please move your source tree to a case-sensitive filesystem. build/core/main.mk:61: ************************************************************ build/core/main.mk:62: *** Case-insensitive filesystems not supported. Stop.
Ah yes, that is an elegant (but slower I would think) solution. I was lucky- I had an external drive I use for TimeMachine. I bit the bullet and partitioned it out and shaved off 30G for my new case-sensitive partition.
The easiest way to do this is to create a disk image to work from that is case sensitive HFS+ and build from there.