Can a Client Running a SQL Server 2005 Express Subscription replicate with
another Client Running a SQL Server 2005 Express subscription? Or Synch with
each other?

Or do you still need a Std SQL Server in the backend to act as the
Publisher/Distributor?

If so do you still need CAL Licenses for SQL Server 2005 Express on the

Express Edition can be a subscriber to publications so you'll need a higher
version of SQL Server somewhere in the mix.
Cheers,
Paul Ibison SQL Server MVP, www.replicationanswers.com .