AFAIK, there's no way to use Personal Profile/NetBeans on the P900. The device comes with Symbian's implementation of Personal Java. You can write a HelloWorld program, and you might want to check out FreEPOC's jCompile program which enables pJava programs to be compiled directly on the machine. It includes a couple of demo programs which may help. See www.freepoc.org.
personal profile is just starting to come out, so to write examples of personal profile, you'll have to either pick up the reference implementation from javasoft.com (a dated copy from late 2002 with some basic samples), or you can use the personal profile plugin beta from nokia (for the nokia 9500, which does run PP) and IBM's device developer studio: