Here's one thing to be aware of. It may not be what's blocking you today, but it's been a factor during our testing.
Vista and Win2K8 changed the protocols associated with remotely accessing file systems. On the Vista box, go to the Administrative Tools and launch the Local Security Policy editor. Expand "Local Policies" and then select "Security Options". Scan down the list for an item called "Network Security: LAN Manager Authentication Level".
On Vista and Win2K8, this is set to "NTLMv2 Responses Only" by default. However this will prevent these Vista/Win2K8 boxes from being able to interact with Win2K, Win2K3 or WinXP since these older Windows platforms do not understand or participate in the newer NTLMv2 protocols.
The full explaination is too much to include in this note, but you can read about the details here: http://support.microsoft.com/kb/823659. You'll find the full details under ithe item labeled "10. Network security: Lan Manager authentication level"