public enum OSVersionEnum : int
{
    /// <summary>
    /// Unknown
    /// </summary>
    Unknown = 0,
    /// <summary>
    /// Microsoft Windows 95
    /// </summary>
    Win95,
    /// <summary>
    /// Microsoft Windows 98
    /// </summary>
    Win98,
    /// <summary>
    /// Microsoft Windows ME
    /// </summary>
    WinME,
    /// <summary>
    /// Microsoft Windows NT 4.0
    /// </summary>
    WinNT4,
    /// <summary>
    /// Microsoft Windows 2000
    /// </summary>
    Win2000,
    /// <summary>
    /// Microsoft Windows XP
    /// </summary>
    WinXP,
    /// <summary>
    /// Microsoft Windows Server 2003
    /// </summary>
    Win2003,
    /// <summary>
    /// Microsoft Windows Vista
    /// </summary>
    WinVista,
    /// <summary>
    /// Microsoft Windows 7
    /// </summary>
    Win7
}

/// <summary>
/// Liefert das aktuelle Betriebsystem.
/// </summary>
/// <returns></returns>
public static OSVersionEnum OSVersion
{
    get
    {
        OperatingSystem os = Environment.OSVersion;
        if (os.Platform == PlatformID.Win32Windows && os.Version.Major >= 4 && os.Version.Minor == 0)
            return OSVersionEnum.Win95;
        if (os.Platform == PlatformID.Win32Windows && os.Version.Major >= 4 && os.Version.Minor > 0 && os.Version.Minor < 90)
            return OSVersionEnum.Win98;
        if (os.Platform == PlatformID.Win32Windows && os.Version.Major >= 4 && os.Version.Minor >= 90)
            return OSVersionEnum.WinME;
        if (os.Platform == PlatformID.Win32NT && os.Version.Major <= 4)
            return OSVersionEnum.WinNT4;
        if (os.Platform == PlatformID.Win32NT && os.Version.Major == 5 && os.Version.Minor == 0)
            return OSVersionEnum.Win2000;
        if (os.Platform == PlatformID.Win32NT && os.Version.Major == 5 && os.Version.Minor == 1)
            return OSVersionEnum.WinXP;
        if (os.Platform == PlatformID.Win32NT && os.Version.Major == 5 && os.Version.Minor == 2)
            return OSVersionEnum.Win2003;
        if (os.Platform == PlatformID.Win32NT && os.Version.Major == 6 && os.Version.Minor == 0)
            return OSVersionEnum.WinVista;
        if (os.Platform == PlatformID.Win32NT && os.Version.Major == 6 && os.Version.Minor == 1)
            return OSVersionEnum.Win7;
        return OSVersionEnum.Unknown;
    }
}

/// <summary>
/// Liefert den Namen des Betriebssytem (z.B. "Windows XP")
/// </summary>
/// <returns></returns>
public static string OSName
{
    get
    {
        switch (OSVersion)
        {
            case OSVersionEnum.Win95: return "Windows 95";
            case OSVersionEnum.Win98: return "Windows 98";
            case OSVersionEnum.WinME: return "Windows ME";
            case OSVersionEnum.WinNT4: return "Windows NT 4";
            case OSVersionEnum.Win2000: return "Windows 2000";
            case OSVersionEnum.WinXP: return "Windows XP");
            case OSVersionEnum.Win2003: return "Windows Server 2003");
            case OSVersionEnum.WinVista: return "Windows Vista");
            case OSVersionEnum.Win7: return "Windows 7");
        }
        return "";
    }
}