I continue to have the same problem, and can't describe it any better than you did.
Same thing, XP and Windows2000. They can ping each other, no mapped drives, the shares are there but invisible.
By recreating stuff (including passwords, workgroup names, TCP/IP check etc), I managed to get W2K machine to actually see XP's shared directory and read and write a file on XP, but it's flaky. And the only way I could do it is through the UNC naming \\192.168.1.xxx\shareName. As before, in Zone Alarm each computer, in fact the entire range, is in the Trusted Zone, but I suspect you're ok here with whatever firewall you use, since you too can ping.
Sorry for no answers, I, like you, keep hoping for some clear steps how to recover from what last M$ updates broke.
Edit: I'm not familiar with VNC. Just used to map them before and it worked both ways.
Edited by tos226, 03 January 2007 - 11:30 PM.