There's nothing specific to USB ports in .NET. .NET gives access to WMI that will allow you to query information about ports and devices.
See http://www.csharphelp.com/archives2/archive334.html for an introduction to WMI in C# (and google for "WMI C#" for lots more).
See http://www.microsoft.com/technet/scriptcenter/resources/qanda/mar05/hey0315.mspx and http://blogs.msdn.com/powershell/archive/2007/02/24/displaying-usb-devices-using-wmi.aspx for examples of querying USB information via WMI (not C# examples).
