The follow up to SQL Server Mobile is now available for download, named SQL Server 2005 Compact Edition now you have a free compact embedded database for single-user client applications for all Windows platforms including tablet PCs, pocket PCs, smart phones and desktops. Yes same bits on all the devices!
http://www.microsoft.com/sql/editions/compact/default.mspx for all information http://www.microsoft.com/sql/editions/compact/downloads.mspx for download.
Have fun!
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.