You'll need several things to get started with iReport:
Sun JDK 1.4 or greater
Ant (required if you want recompile sources, but strongly reccomended to lunch iReport too)
JasperReports 0.4.6 (*)
SAX 2.0 XML Parser (Apache Xerces 1.3 or later recommended) (*)
Jakarta Commons Digester Component (version 1.1 or later) (*)
Jakarta Commons BeanUtils Component (version 1.1 or later) (*)
Jakarta Commons Collections Component (version 1.0 or later) (*)
Jakarta Commons Logging Component (version 1.0 or later) (*)
JDBC 2.0 Driver (A MySql driver is already included) (*)
iText - Free Java-PDF library by Bruno Lowagie and Paulo Soares (*)
Jakarta POI (version 1.5.1 or later) (*)
JFreeChart (version 0.9.8 or later) (*)
Acrobat Reader 5.0 is not required, but strongly recommended.
If you think to use Chinese Simplified, Chinese traditional, Japanese and Korean characters, you must download the Asian font pack from Adobe at: http://www.adobe.com/products/acrobat/acrrasianfontpack.html or use a localized Windows.
If you want connect to a database, you must provide a JDBC driver (not shipped with iReport).