The problem with SAP is that, while it can use a 'standard' database like Oracle, it stores its data in such a mangled way as to be inaccesible to others. So direct DB access is out. Your best bet would probably to define an interface file for example, and communicate though that with an ABAP4 program on the SAP side. Good luck.
You most definitivedly will need access to someone with good SAP knowledge to manage the SAP side. SAP tries to push new technologies like NetWeaver and mySAP suite which are J2EE or .net based. Personally I know nearly nothing about those. And for sure its not easy, because SAP in general is no piece of cake. If you use an appServer J2C (Java 2 Connector Architecture) might help. IBM and other J2EE vendors do have some information about best practices with SAP-integration. 4 years ago my then company was involved in a bigger SAP integration proyect with Lotus Notes. There was a clear separation: our guys/gals did the lotus notes part, other company did SAP side.
subject: How to link to SAP through an Application