How can I make this code read a page every 10 seconds?
As discussed in the comments, you need to connect to the client each time, not just once.

Here's my modified version of your code, which I hope will work -- I'm not set up to test it.

#include &lt;Ethernet.h&gt;
#include &lt;SPI.h&gt;

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip[] = { 192, 168, 1, 104 };
char server[] = "billigefittings.dk";

void setup()
{
  Ethernet.begin(mac, ip);
  Serial.begin(9600);

  delay(1000);

  Serial.println(Ethernet.localIP());
  Serial.println();
}

void loop()
{
  // Connect to the server
  Serial.println("connecting ...");

  EthernetClient client;
  if (client.connect(server, 80)) {
    Serial.println("connected");
    client.println("GET /lan.php");
    client.println();
  } else {
    Serial.println("connection failed");
  }

  // Wait a moment for data to arrive
  // Note: This is NOT a reliable way of doing it!
  delay(1000);

  if(client.available() &gt; 0) {
    char c = client.read();

    Serial.print("page value:");
    Serial.println(c);

    if(c == '1') {
        digitalWrite(8, HIGH);      
        Serial.println("8 HIGH ...");
        delay(5000);
        digitalWrite(8, LOW);
        Serial.println("8 LOW ...");
    }else{
        Serial.println("page value does not match '1' !");
    }
  }

  // Disconnect the client    
  if(client.connected()) {
    Serial.println();
    Serial.println("disconnecting.");
    client.stop();
  }

  // Wait another 9s, which will give us a delay of roughly 10s
  delay(9000);
}