How do I check if an NTAccount object represents a Group or a User?

Question

When working with the access rules returned by

GetAccessRules(True, True, GetType(System.Security.Principal.NTAccount))

how can I tell if the NTAccount object referenced in each rule is a user account or a group?

Update:

I was able to solve this as follows. Note, the intent of this code is to return True if the NTAccount is a group, and False otherwise or if an error occurs during checking.

Is there a better way to do this?

Public Function IsGroup(ByVal account As NTAccount) as Boolean  
    Dim samAccountName as string = account.Value  
    Dim accountNameParts() As String = samAccountName.Split("\")  
    If accountNameParts.Count() = 2 Then  
        Dim principalContext As PrincipalContext  
        Try  
            principalContext = New PrincipalContext(ContextType.Domain, accountNameParts(0))  
        Catch  
            Try  
                principalContext = New PrincipalContext(ContextType.Machine, accountNameParts(0))  
            Catch  
                principalContext = Nothing  
            End Try  
        End Try  
        If Not principalContext Is Nothing Then  
            Dim principal As Principal  
            principal = principal.FindByIdentity(principalContext, _samAccountName)  
            If Not principal Is Nothing then   
                return TypeOf principal Is GroupPrincipal  
            End If  
        End If  
    End If  
    Return False  
End Function

Another update:

The above solution was okay for most server\account objects, but it fails for local group objects on the EMC Celerra NAS servers we have. I'm trying to use the NetUserGetInfo/NetLocalGroupGetInfo Win API calls to see if that will work, but I can't get them to work properly. See http://stackoverflow.com/questions/3663571/netusergetinfo-netlocalgroupgetinfo-returning-error-1722 for more details.