Community
Check out the AutoCAD .NET Developer's Guide on Autodesk Exchange: http://exchange.autodesk.com/autocad/enu/online-help/browse#WS1a9193826455f5ff2566ffd511ff6f8c7ca-48...
Specifically, you may want to check out the GetPoint example to get you started: http://exchange.autodesk.com/autocad/enu/online-help/browse#WS1a9193826455f5ff2566ffd511ff6f8c7ca-42...
Cheers,
Drew