I was having this issue...feel like an idiot now. I didn't actually install the jdk
! Surprisingly I got as far as building and testing the RIM Samples and my own application with no problem. It wasn't until I went to test using a project that depends on another project. I'm guessing at this point Eclipse needed "jar" to put together the compiled code from the separate projects.
Anyway, once I installed the jdk I still wasn't quite there. I had to edit my Windows Environment PATH variable to have the path to the jdk bin directory. In my case it was:
Save the variable change. Restart eclipse, and presto, off to the races.