Packet Sniffer SDK for Windows 4.1 is  your excellent choice. Its component/library family allows you to use the full power of any modern visual or non-visual development environment for creating various packet capture network applications working with raw network adapter or loopback traffic.

Using Packet Sniffer SDK the developer does not need to create special network drivers or to learn internal implementation of the network functionalities in all Windows family operating systems - Packet Sniffer SDK allows you to focus on the main task which your application must solve.

Main Packet Sniffer SDK elements are developed as objects with properties, methods, and events that make the packet capture applications development process simpler and more flexible.

To simplify the usage of LIB and DLL Packet Sniffer SDK library implementations, special wrapper classes are created, in which functions for working with PSSDK objects are represented as class methods.

Major Features:

1. NET wrapper for PSSDK objects: Packet Sniffer SDK package is provided with .NET wrapper for PSSDK objects source texts. This wrapper allows to integrate and use PSSDK with .NET applications with easy, and may be used in any development environment supporting .NET technology.
2. Support of BPF: Packet Sniffer SDK supports packet filtering by BPF (BSD Packet Filter, user-settable packet filters) at the level of the built-in packet capture driver.
3. Support of FastBPF: Packet Sniffer SDK supports new FastBPF technology (Just-In-Time BPF filters compilation). FastBPF works approximately 6 times faster than classic BPF filtering by BPF virtual machine.
4. No pre-installed packet capture drivers are required: All editions of the Packet Sniffer SDK contain internal packet capture driver, which is dynamically loaded when the application is launched. When your application is started, it loads and launches built-in packet capture driver. When your application is closed, built-in packet capture driver is unloaded. This feature of PSSDK allows to create portable applications which may be launched from removable devices without installation on the user's PC.
5. Support of Gigabit networks: You can create an application to capture Gigabit network traffic with zero packet loss. Certainly, your success depends on CPU, RAM, HDD subsystem performance, etc.
6. Support of multiprocessor (SMP) systems: Packet Sniffer SDK supports symmetric multiprocessing platforms with near linear performance dependance on additional CPU resources.
7. Packet generating/sending functions: This feature allows to create and send packets with any structure. It may be very useful if you're going to develop network security scanner with non-intrusive vulnerability detection capabilities, or application using its own non-standard protocol.
8. WinPCap to PSSDK migration module: Allows easily (in hours) migrate libpcap/WinPCap-based projects to Packet Sniffer SDK.
9. Capturing of TCP/UDP traffic, loopback support. With PSSDK you can capture TCP sessions and reconstruct them in TCP data streams. Also localhost TCP sessions capturing with binding them with local processes is supported.
10. BPF assembler and disassembler: To increase readability of your BPF programs your can write them in BPF Assembler, also you can disassemble existing BPF filters in human-readable format.