OS X :: Finder No Longer Showing Windows Network?

I hope that this post is original, but if not I apologize. I did some searching, but found nothing specifically in the area where I'm having networking problems.First, I very much enjoy using the newest MacMini (10.6). I got it a few months ago, and have been slowly migrating from Windows. This is where I am having difficulty solving an issue.

In the beginning I was able to network the three computers I have together and was able to "see" the two windows machines in the Finder under "network"; the laptop (Vista) and the desktop (XP). Soon there after, the Finder stopped listing the two windows machines in the Finder's "network" category. The odd thing about this issue is that by this point in time I was able to "see" the Mac from both Windows machines (dragging files from windows to the mac), but not the other way around.

Now, and the reason for this post, neither lists each other (Mac vs. Windows). I can still "see" the windows machines from each other's Explorer, but alas not the Mac.To wade through allot of questions that may crop up, I have gone through all three machine's networking "sharing" setups, and I cannot locate where the problem lies. I can also use the networking utility from the Mac and be able to "ping" the other machines. I can use Safari and "address" (http) pages from the machines, but nothing in the way of "drag-n-drop" files from the Finder.I greatly appreciate this forum, and in other areas I was able to solve other issues.