Hi Dave,

>1) Which development edition of SQL Server is most suitable for developing solutions off-site (without access to a client's enterprise or standard edition of SQL Server)? Is SQL Server 2000 Desktop Engine suitable for this?

That's exactly what the Developer Edition is for. MSDE is good for clients who have a small number of users and a small amount of data so they won't have the expense of a full SQL Server license.

>2) What is involved in upgrading an application (developed with SQL Server Desktop Engine) to a client's full SQL Server system? Is this just a simple process of copying the application's database files/tables on to the client's hard drive/server? Or, is something else involved?

MSDE is exactly the same as SQL Server except a) it doesn't have the nice GUI administration tools (although you can use the tools from the Developer Edition), b) it's "crippled" to slow down with more than a handful of active users, and c) it's limited to 2GB per database.

You can read more at
http://www.microsoft.com/sql/techinfo/planning/SQLReskChooseEd.asp

There's a new, free web-enabled administration tool which should make up for the lack of a GUI tool for MSDE:
http://www.microsoft.com/downloads/details.aspx?FamilyId=C039A798-C57A-419E-ACBC-2A332CB7F959&displaylang=en