This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Is your server expecting text or a JavaString object? Using an Object Output Stream will serialize a Java String Object.
You should probably take a few moments and run through the Java Socket Tutorial and the Java IO Tutorial. A solid base in those two features is essential for working with sockets.