Calling C# class from VB.NET

Hi
For various reasons I need to access a C# class from within a VB project. The C# class calls an API.dll which returns fixed types which are not supported in VB.NET so the idea is to get the C# module to convert these before returning values to VB

So here's the problem - how do I get to access the C# clas in VB.NET the class is
public class API
    {
        // ¤Þ¥Î Fritz DLL
        [DllImport("DllApCli.dll")]
        public static extern void DebugMsg(int bOn);
        [DllImport("DllApCli.dll")]
        public static extern void ApOpen();
        [DllImport("DllApCli.dll")]
        unsafe public static extern int ApConnectToServer(string szSrvIP, int dwSrvPort);
        [DllImport("DllApCli.dll")]
        unsafe public static extern int ApGetVersion(out int iMajorVer, out int iMinorVer);
        [DllImport("DllApCli.dll")]
        public static extern int ApMessageCount(int hAP);
        [DllImport("DllApCli.dll")]
        public static extern void ApClose();
        [DllImport("DllApCli.dll")]
        public static extern int ApEraseAllMessage(int hAP);
        [DllImport("DllApCli.dll")]
        public static extern void ApDisconnect(int hAP);
        [DllImport("DllApCli.dll")]
        unsafe public static extern int ApGetMessage(int hAP, out long dwUnitID, out int dwMsgID, byte* szBuff, int iBuffLen);
        [DllImport("DllApCli.dll")]
        public static extern int ApAttachCount();
        [DllImport("DllApCli.dll")]
        unsafe public static extern int ApSendCmd(int hAP, long dwUnitID, byte[] szCmd, int iCmdLen);
        [DllImport("DllApCli.dll")]
        unsafe public static extern int GetNumberOfCleint();
    }

An example of the ApSendCmd method as called in a C# project is shown below

        public void SendMessage(string Message)
        {
            int IsOK;
            byte[] Msg = Encoding.Default.GetBytes(Message + "\r\n");

            IsOK = API.ApSendCmd(m_hAP, System.Convert.ToInt32(tvOBUGroup.SelectedNode.Text), Msg, Msg.Length);

            switch (IsOK)
            {
                case 0:
                    tbConsole.Text += "Send message failed." + "\r\n";
                    break;
                default:
                    tbConsole.Text += "Send " + Message + " to " + tvOBUGroup.SelectedNode.Text + "\r\n";
                    break;
            }
        }

How do I replicate this functionality in a VB.Net app?

Many thanks