ENC28j60 ethernet interfacing with PIC18F4520 help needed
Yes this is possible with TCP/IP stack. I think you should not directly jump into reading some sensor data and send it to server every 3 minutes, instead try to build the demo app provided by Microchip and access their webpage (or your own page).

Microchip provide TCP/IP library which is included in Microchip Application Libraries v2013-06-15(MAL). Download and install MAL on your system. Build the the TCP/IP demo app and upload it on your MCU. Connect the LAN cable between ENC28J60 and your PC. If everything went ok, then you can open the TCP/IP Discoverer Tool which is found in C:\microchip_solutions_v2013-06-15\Microchip\TCPIP Stack\Utilities, to get the IP address. Enter the IP address in your browser and you can access their default webpage.

Now next thing you have  to do is build your own webpage and put all web files inside webpages folder. So next time when you enter the IP address in browser, it will open your webpage. In the code you will have to put some dynamic variables to get and post data to your webpage. I cannot explain everything here. But you can read below tutorials which include everything you want.

Part 1: Web based monitoring

Part 2: Web based control

Part 3: Advanced web based control

You can watch these video tutorials for step by step explanation tutorial1 tutorial2 tutorial3