Net Weaver in simple words is an application and Integration platform in which Web Services play a major role and which is open for Non-SAP applications and platform. It is an another Eclipse RCP (Rich Client Platform) application. In near future, can be extended with, and inter-operate with, technologies such as Microsoft .NET, Sun Java EE, and IBM WebSphere. According to your background it is better to go for SAP-BI and visit here for more information
OR you may go for SAP Web AS Java Administration.
But, always consult with your nearest people or ask for consult firm regarding your question.