Adding IP Address To ListView - Get Return Value

I have a Callback from a socket that get called each time I get a Packet, It then add an IP address to a Listview. Now I got all the IP with the Active Connections, I cannot, From the call back check if the IP is already added to the list so I made a class and a Delegate and used UI.Invoke to call the method and check if Duplacates then add the coordinating information, I went a Step further and did a lookup on host name to pull the computer hostname from the ipaddress, But I do it each time due to getting Multiple of the same IP and I do not want to do it on the thread that the UI.INvokes from due to resolving a Host name will lock the GUI for a full Second, so you can imagine doing this on a network with constant information.

Now what I want is from the Async thread that is receiving all the data to Invoke the UI thread, check if ListviewItem already exist then exit the Dispatched Sub, then from the Async thread again check the Classes return value then if it dose not already exist start the lookup, I have this so far but Im not 100% sure if it is working the right way, Is Invoke Async or Sync even though Im telling another thread to start, if now how can I made My Async thread wait on UI.Invoke to complete 100% so I can check the classes return value?

Async Thread
Code:
MySubPtr = AddressOf MyDispatch.TreeViewItemExist 'Trigger The Event Through Form1 Backed Up Handle!
Try
'Dim DoesTheItemExist As IAsyncResult
'IAsyncResult = MainHandle.BeginInvoke(MySubPtr)
[Code] .....