two trees in a forest

I have a test lab set up with 2 win 2000 domain controllers and a linux router.One DC is x.com the 2nd dc is y.com. I joined y.com to the existing forest as a seperate domain.
Everything works fine except in network neighborhood on y.com …only y.com can be seen. But on the forest root dc(x.com) in network neighborhood I can see x.com and y.com. I can browse active directory and see both. Why can I not see both domains on y.com in network neighborhood?