How do I debug threads using eclipse?

I have a bug in one of my threads, but I can't step to it for some
reason. Here is an example:

class A{

Thread thread = new thread(B);
thread.start(); //breakpoint1

...
}

class B implements Runnable{

run(){

blah blah // breakpoint 2

}

If I step into (F5) breakpoint 1, it doesn't go into the run method of
class B.

If I try to run to next breakpoint, it just runs till the end of the
program.

Now I know that the thread is executing because I get a partial ouput
from it, but it is incorrect.

So how do I step into a different thread of execution?

Thanks a lot,
Ben