Installation of SAP J2EE engine standalone version

For administiring J2ee on the WebAs, SAP recommends installing the J2ee engine standalone version on a PC. Where can we find the standalone version? In case, i use the J2ee engine CD available with WebAs, which mode of installation should i choose (1 - For existing Central Instance, 2 - Dialog Instance, 3 - Gateway Instance).

Can anybody help with this query?