Which SQL Product? Everywhere Or Express

We are building a system that has mobile clients (laptop with XP and tablet with XP). These clients have data moving back and forth to a centralised n-tier server based system. The communications is proprietory and are very low bandwidth (5 KByte/sec).

We've decided that the best approach to handling both the reference data (ranging from trivial to a complex list of items - about 2 million rows) and the day-to-day operational data is with a database product rather than attempting to handle it ourselves within code.

The question is - what SQL platform to use? SQL Everywhere seems to be a fairly good choice except that it does not seem to support stored procedures. SQL Express is another possibility but there are concerns about the size of the footprint and managing the database engine and the database itself.

The users of the mobile client are considered computer illiterate and would not be able to manage any database administrative tasks. They only come back to base every three to six months. History has shown remote management of the machine has proven difficult (if not impossible) via the low bandwidth connection.

The machines have 512MB of RAM and only 40GB of disk. They have to support XP, Office, our client, and our GIS client. What is the best answer?

Traditionally we would have used MSDE.

Regards
Paul