This is happening with all my 2008 servers.
You have multiple virtual 2008 servers? Were they cloned? Were they converted from a physical machine(s)? You have them all on at the same time or just one VM on at a time?
Either on DHCP or a statically assigned address and no, the (static) addresses are not in use. DHCP should be independent anyway, a new request for an IP.
I can't tell you how many times I or my coworkers have wasted hours of overtime because "it's not supposed to do that." 
So when on DHCP, have you released/renewed? If these VMs are copies then they may have the same MAC addr which means DHCP issues the same IP addr. Do you have any machines that are not giving a duplicate IP error? From one of those machines, can you still PING the duplicate IP even with the 2008 machines off?
IF your absolutely certain 100% without doubt that this IP does not exist, (Are you sure that there's been no Windows update or registry restore that has reenabled the Windows firewall?) Which is why I say if a software firewall was inadvertently reenabled, then a a PING test would be insufficient. Thus, going to each machine and checking it's IP at it's console.
If as you say, you've built 2008 VMs on Server that worked, then copy this non-working VM to Server. (Downgrade the virtual hardware first, if necessary.) If it works on Server, then you can suspect something with WS or the configuration of the WS host. If it doesn't work, then you know that your VM is the problem.
You don't give much specifics (PING results from 2008 machine, PING results from XP VMs, PING results from VMs on different host. IPCONFIG, VMX file, etc.) so it's difficult to troubleshoot more. But what I was mentioning previously is to try to see if you're making any assumtions. (Why do you check this box in networking properties? Because I've always used that. But why? ) To paraphrase Sherlock Holmes, if all logical suspects have been eliminated, then start looking for illogical suspects. Meaning, just because you've been able to make 2008 VMs that worked before, does not mean that this VM not working must be a bug in WS. Confirm that this VM is working. Confirm that there are no dup IPs. I usually start my troubleshooting with the phrase "what have I done wrong?" instead of "what's wrong with this thing?!" which helps me find one of my stoopid mistakes more quickly. :smileyblush:
You have Server on one network, but Workstation on another network. So you have not tried the same VM in Workstation AND Server on the SAME network. (Assumption: the two networks are identical.) So install Server on your problem network and copy the non-working VM to the Server host. If problem still happens on Server, then the issue is NOT a bug in Workstation. The rule when troubleshooting is to change ONE thing at a time, not multiple things.
Not stated: did you COPY the non-working 2008 VM from the Workstation network to the Server network? Not build a new 2008 VM, but copy the existing one? (e.g.: your Toyota starts up this morning, therefore your friends's Toyota will start this morning. No, because they're different machines.)
Assupmtion: " I KNOW the static IPs being assigned ARE NOT on the network." No rogue machines that you forgot about or someone else didn't tell you about? (If no one told you, how do you know? ) It's only 6 machines so it's you can physically go to each machine and check. Multihomed NICs? Printservers? Webcams? Or just turn off all machines. Obviously, if the machine is off, there can't be a dup IP error. Simple tests that don't take much time and will very quickly eliminate these possibilities.
Not stated: working XP machines are using the SAME IP addr as the non-working 2008 machines? If different IP addr, then that is not testing anything about dup IP addr.
I've installed 2008 (32bit) as a VM and run it in WS6, WS6.5beta, Server1 and Server2 beta. The one major difference between my setups and yours is that my hosts are Windows based, no Linux. (XP-Pro, Vista Business, 2003 Server hosts.) But you said your WS6.0.3 was using Vista as a host so that (probably) rules out a specific Linux host issue.
I'm repeating because in my experience, many of these issues are because people do the same things over and over, not realizing that they're making the same mistakes. I have not seen any dup IP thread regarding 2008 VMs. And WS6 has been out for a while so based upon what's been posted, there is not enough evidence to point to a bug in Workstation. My point is that there are many assumptions that you've made (or implied in your posts) that have not been eliminated.
