Refactored the code from balexandre a little so objects gets disposed and the new language features of C# 3.5+ are used (Linq, var, etc). Also renamed the variables to more meaningful names. I also merged some of the functions to be able to do more configuration with less WMI interaction. I removed the WINS code as I don't need to configure WINS anymore. Feel free to add the WINS code if you need it.
For the case anybody likes to use the refactored/modernized code I put it back into the community here.
/// <summary>
/// Helper class to set networking configuration like IP address, DNS servers, etc.
/// </summary>
public class NetworkConfigurator
{
    /// <summary>
    /// Set's a new IP Address and it's Submask of the local machine
    /// </summary>
    /// <param name="ipAddress">The IP Address</param>
    /// <param name="subnetMask">The Submask IP Address</param>
    /// <param name="gateway">The gateway.</param>
    /// <remarks>Requires a reference to the System.Management namespace</remarks>
    public void SetIP(string ipAddress, string subnetMask, string gateway)
    {
        using (var networkConfigMng = new ManagementClass("Win32_NetworkAdapterConfiguration"))
        {
            using (var networkConfigs = networkConfigMng.GetInstances())
            {
                foreach (var managementObject in networkConfigs.Cast<ManagementObject>().Where(managementObject => (bool)managementObject["IPEnabled"]))
                {
                    using (var newIP = managementObject.GetMethodParameters("EnableStatic"))
                    {
                        // Set new IP address and subnet if needed
                        if ((!String.IsNullOrEmpty(ipAddress)) || (!String.IsNullOrEmpty(subnetMask)))
                        {
                            if (!String.IsNullOrEmpty(ipAddress))
                            {
                                newIP["IPAddress"] = new[] { ipAddress };
                            }
                            if (!String.IsNullOrEmpty(subnetMask))
                            {
                                newIP["SubnetMask"] = new[] { subnetMask };
                            }
                            managementObject.InvokeMethod("EnableStatic", newIP, null);
                        }
                        // Set mew gateway if needed
                        if (!String.IsNullOrEmpty(gateway))
                        {
                            using (var newGateway = managementObject.GetMethodParameters("SetGateways"))
                            {
                                newGateway["DefaultIPGateway"] = new[] { gateway };
                                newGateway["GatewayCostMetric"] = new[] { 1 };
                                managementObject.InvokeMethod("SetGateways", newGateway, null);
                            }
                        }
                    }
                }
            }
        }
    }
    /// <summary>
    /// Set's the DNS Server of the local machine
    /// </summary>
    /// <param name="nic">NIC address</param>
    /// <param name="dnsServers">Comma seperated list of DNS server addresses</param>
    /// <remarks>Requires a reference to the System.Management namespace</remarks>
    public void SetNameservers(string nic, string dnsServers)
    {
        using (var networkConfigMng = new ManagementClass("Win32_NetworkAdapterConfiguration"))
        {
            using (var networkConfigs = networkConfigMng.GetInstances())
            {
                foreach (var managementObject in networkConfigs.Cast<ManagementObject>().Where(objMO => (bool)objMO["IPEnabled"] && objMO["Caption"].Equals(nic)))
                {
                    using (var newDNS = managementObject.GetMethodParameters("SetDNSServerSearchOrder"))
                    {
                        newDNS["DNSServerSearchOrder"] = dnsServers.Split(',');
                        managementObject.InvokeMethod("SetDNSServerSearchOrder", newDNS, null);
                    }
                }
            }
        }
    }
}