The Spring '10 release of the Force.com IDE contains the
following major new features:

• Eclipse 3.5 Support
  • Use the Force.com IDE with Eclipse Platform 3.5 (Galileo).
• New Metadata Support in Spring '10
  • Business Processes
  • Entitlement Templates
  • Data Category Groups
  • Enhancements to Schema, Dashboards, Reports, Workflow and more,
    including Action Overrides, Lookup Filters, and List Views on Standard
    Objects.
• Documentation and User Assistance
  • All documentation has been updated with Spring '10 content,
    including the new Force.com Workbook based on the Warehouse application.

For more information, see the Force.com IDE Release Notes.

To
get started, visit the installation instructions for Eclipse 3.5.