Web Service Network Credentials in Workgroup setup

 I have a couple machines running web services in a non-domain workgroup setup. I'm trying to use Windows Integrated security between the two machines to prevent anonymous access.
When calling a web service on a different machine I've been attempting to use the CredentialCache object like so:
cache.Add(New Uri(service.Url), "Negotiate", New NetworkCredential(username, password))
service.Credentials = cache
But I keep getting a 401: Unauthorized error.
Is there a way to properly configure this for a workgroup setup?
Thanks.
Kel
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