How can I enable an encrypted network connection to SQL Server? What have I to do on the client and on the server side?
You can let the operating system take care of it via an IPSEC policy. With SQL Server, you must have a trusted SSL certificate, but here's how: Books Online - How to: Enable Encrypted Connections to the Database Engine.
You can configure via server/client network utilities: http://support.microsoft.com/kb/316898
You still need certificates, and to specify encryption in the connection string. We use an offline CA to generate our certificates using OpenSSL, and then install on the clients and server w/ MMC.