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.
As you've discovered, you can't nest tags like that--that's simply not valid JSP. You'd need to set the value to a variable and use either JSP 2+ EL, or the Struts EL tags if you're not running in a JSP 2+ container.