I've been going nuts over this for a week! I've tried so many solutions and registry hacks that I've lost track.
Here's what I have and what's been happening:
I'm building a new SBS 2003 server and a Server 2003/SQL box. These 2 are on their own switch so as to not interfere with my production SBS server. I have 1 Win XP box on this Pre-Production LAN. I have VNC (free version) fresh from the their site installed on all three: KAS-SBS, KAS-SQL, and KAS-101. All 3 computers are completely patched with everything MS has to offer. Here are the results:
SBS and SQL can see each other with VNC.
SBS and SQL cannot see 101 with VNC.
101 can see both SBS and SQL with VNC.
Using RAS/VPN to connect to SBS, I cannot see 101.
I've been concentrating on SBS because VNC works perfectly in the production environment. I've rebuilt SBS a couple of times but currently I do not even have ISA installed. I've even rebuilt 101 and kept it out of the domain.
The solution for was too simple to see. After reading this article, I disabled Windows Firewall on the XP box and now VNC works in all cases (I haven't tested remote access yet).
VNC uses port 5900 (5800 for a 1-time Java hit) so I suppose i can try opening that port on the XP box. But eventually I will have ISA running on SBS so that will just be an experiment for my own satisfaction.
I hope this helps save someone from banging his head against a door!
~Dave