Vista - The usual - Vista/XP network problem

I'm at my wits end! I have read forums until I am blue in the face. I've tried everything everyone has suggested (assuming I did it correctly, however), and I'm still having problems.

Here's the story: 4 XP computers and 1 Vista computer - all Ethernet connected
All can use the internet OK. All XP computers see each other and can share files and printers OK. Vista machine does not display XP machines in "Network and Sharing Center/View computers and devices."

I can ping the other computers successfully and Network Magic displays all information about them in their map. In Explorer, under Network, on the Vista machine, only the Vista machine shows up with its shared folders.

All computers share the same workgroup name
XPs use Zone Alarm and Vista machine uses Windows firewall (Vista machine was using Zone Alarm also until a recent problem developed causing Firefox to hang - but this network issue was present then also)
Router is Linksys WCG200
It's a private network
File/printer sharing are on
Network discovery is on
Public folder sharing is on
Password protected sharing and media sharing are OFF

There was a time a month, or so, ago when this whole setup worked. I don't know what I did (or some download/update did) that might have changed something.

Let me know if I missed supplying some information.

Any help will be IMMENSELY appreciated! Thank you in advance.

I'm having exactly the same problem! In stead of 4 XP computers I've only one (laptop wifi connected) a dreambox (over LAN working on Linux) and sometimes a mobile telephone (widows mobile over wifi). From the XP everything is working fine, network printing, filesharing, streaming to the dreambox, I see all network members (even if they are not in the same workgroup), everything works perfectly. From Vista I only see the Vista desktop and the router in the network explorer. I can ping all network members without problem. I even can connect to the dreambox, streaming media to it ect. Since from XP everything works, and from Vista I also can't see a Linux member, I'm quite sure the problem is in Vista.
Same as Ramjet also here there was a time everything used to work fine!
Is this problem so hard to solve that nobody answer this Thread for more than a week?
Please help us out!!
Thanks in advance