How to get php variable from url (href link) in javaScript and generate a small popup window on mouseover with passed php data

The answers to all of these questions are already here on SO. Break your problem down into smaller steps and you will find it:

• How to call a script with mouseover
• How to make a modal dialog using JavaScript + CSS
• How to pass data between JavaScript and PHP

The easiest solution is to use ajax. Here is a sample implementation:

1. The url link should contain the data you want to send to the server and would look like:

   <a href="yourURL" onclick="sendURL2Srvr(this);">link text</a>

2. create a javascript section to receive the server response in a popup. This should roughly look like:

   <script>
     http = false;
   
     if (window.ActiveXObject) {
       http = new ActiveXObject("Microsoft.XMLHTTP");
     }
     else if (window.XMLHttpRequest ) {
       http = new XMLHttpRequest();
     }
     function sendURL2Srvr(elem) {
       http.abort();
       http.onreadystatechange=function() {
         var popupW=window.createPopup();
         if(http.readyState == 4) {
           if (http.status != 200)
             error('Something went wrong!');
           else
             popupW.innerHTML=http.responseText;
         }
       }
       http.open("GET", elem.href, true);
       http.send(null);        
     }
   </script>
   

3. It is up to the server to dissect the received REQUEST and send the data back. This now becomes a pure php question.