I have a gps sending data to mysql db, but am having hard time ploting the values on google map. My javascript skills are not very good, pls help...

javascript code

<?php 
    $server = "localhost";
    $username = "root";
    $database = "";
    $password = "";
    $conn = mysql_connect($server,$username,$password);
    mysql_select_db($database) or die("Unable to select database");
    ?>

    <html>
    <head>
    <script type='text/javascript' src='jquery-1.6.2.min.js'></script>
    <script type='text/javascript' src='jquery-ui-1.8.14.custom.min.js'></script>
    <style>

        BODY {font-family : Verdana,Arial,Helvetica,sans-serif; color: #000000; font-size : 13px ; }

        #map_canvas { width:70%; height: 70%; z-index: 0; }
    </style>
    <script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false" /></script>
    <script type='text/javascript'>

    //This javascript will load when the page loads.
    jQuery(document).ready( function($){

            //Initialize the Google Maps
            var geocoder;
            var map;
            var markersArray = [];
            var infos = [];

            geocoder = new google.maps.Geocoder();
            var myOptions = {
                  zoom: 100,
                  mapTypeId: google.maps.MapTypeId.ROADMAP
                }
            //Load the Map into the map_canvas div
            var map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
            map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);

            //Initialize a variable that the auto-size the map to whatever you are plotting
            var bounds = new google.maps.LatLngBounds();
            //Initialize the encoded string       
            var encodedString;
            //Initialize the array that will hold the contents of the split string
            var stringArray = [];
            //Get the value of the encoded string from the hidden input
            encodedString = document.getElementById("encodedString").value;
            //Split the encoded string into an array the separates each location
            stringArray = encodedString.split("****");

            var x;
            for (x = 0; x < stringArray.length; x = x + 1)
            {
                var addressDetails = [];
                var marker;
                //Separate each field
                addressDetails = stringArray[x].split("&&&");
                //Load the lat, long data
                var lat = new google.maps.LatLng(addressDetails[1], addressDetails[2]);
                //Create a new marker and info window
                marker = new google.maps.Marker({
                    map: map,
                    position: lat,
                    //Content is what will show up in the info window
                    content: addressDetails[0]
                });
                //Pushing the markers into an array so that it's easier to manage them
                markersArray.push(marker);
                google.maps.event.addListener( marker, 'click', function () {
                    closeInfos();
                    var info = new google.maps.InfoWindow({content: this.content});
                    //On click the map will load the info window
                    info.open(map,this);
                    infos[0]=info;
                });
               //Extends the boundaries of the map to include this new location
               bounds.extend(lat);
            }
            //Takes all the lat, longs in the bounds variable and autosizes the map
            map.fitBounds(bounds);

            //Manages the info windows
            function closeInfos(){
           if(infos.length > 0){
              infos[0].set("marker",null);
              infos[0].close();
              infos.length = 0;
           }
            }

    });
    </script>

php code

         //Initialize your first couple variables
        $encodedString = ""; //This is the string that will hold all your location data
        $x = 0; //This is a trigger to keep the string tidy


                    //Now we do a simple query to the database
              function dec($dec)

                {
                    $dir=substr($dec, -1);

                    $deg=substr($dec, 0, 2);
                    $mins=substr($dec, 2);

                    $min = $mins / 60;

                    $map=$deg+$min;

                    if ($dir == "S" || $dir == "W") {
                        $map = "-".$map;
                    } // Don't do anything for N or E

                    return round($map, 7);
}
        //Now we do a simple query to the database
        $result="SELECT * FROM `poi`";
        $results = mysql_query($result);
        //Multiple rows are returned
        while ($row = mysql_fetch_array($results))
        {

            //This is to keep an empty first or last line from forming, when the string is split
            if ( $x == 0 )
            {
                 $separator = "";
            }
            else
            {
                 //Each row in the database is separated in the string by four *'s
                 $separator = "****";
            }
                            $dec_lat=$row['lat'];
                            $dec_lon=$row['lon'];

                    //convert lat n lon
                            $lat=dec($dec_lat);

                            $lon=dec($dec_lon);

                            echo$lat.",".$lon;

            //Saving to the String, each variable is separated by three &'s
            $encodedString = $encodedString.$separator.
            "<p class='content'><b>Lat:</b> ".$row['lat'].
            "<br><b>Long:</b> ".$row['lon'].
            "<br><b>Name: </b>".$row['name'].
            "<br><b>Address: </b>".$row['desc'].
            //"<br><b>Division: </b>".$row[5].
            "</p>&&&".$row['lat']."&&&".$row['lon'];
            $x = $x + 1;
        }

am at a lot as to how to get lat and lon values to show on map...

The best approach to work with dynamic google maps is by using json or xml to populate the map with markers. Both solutions are suitable for your needs.

Google publish a great tutorial with examples and code snippet that will help you a lot

Plus, if you wish to know more about how to store and retrieve marker positions (lat, lng) from a mysql DB, feel free to download and explore my phpGmap script here