Orcas beta install fails error code 1603

I've been trying to install an Orcas Beta. I've tried both beta 1 and beta 2
and they both fail with the same error:

Windows Mobile 5.0 SDK R2 for Pocket PC: [2] Error:
Installation failed for component Windows Mobile 5.0 SDK R2 for Pocket PC. MSI returned error code 1603

I don't know why it's even attempting to install this SDK since I'm doing
"custom" install and unchecking everything I don't need, including all of the
"smart device" SDKs.

[537 byte] By [mTIE] at [2008-1-8]