What kind of data to you want to send?
Do you want to use HTTP protocol or TCP or UDP?
Do you have already chosen the microcontroller?
Anyway, the simplest way is most likely the ENC28J60 module and Arduino or something.
The simplest way would to be setup a HTTP server on one computer in the LAN and let all your ENC28J60 connect to it and send data to php script.
For example:
192.168.0.1/myScript.php?key=value
This is the GET request (I might have confused syntax), but you see the data is in the link.
You can also send it by POST request. Then it's a bit more complicated.
On the server side, you write a PHP script and process data there. For example:
Code:
$received = $_GET['key'];
// now do whater you want with $received,
you can insert data to MySQL database or write to file, all in PHP code.
HINT: Search for "Arduino ENC28J60 HTTP CLIENT" code. For this purpose I think you need a HTTP CLIENT on MCU, and HTTP server on single PC in lan.