trying processing data form

Hello to everyone. Well i am new in making plugins and on top of that i have to make one for a project i am into. I’m trying my best but it seems that i lack serious knowledge. Here is my first big problem. The following code is called in the admin’s menu and has 3 possible options.

<form id="form" name="form" method="post" action="process.php">
  <table width="400">
    <tr>
      <td><label>
        <input type="checkbox" name="CheckboxGroup[]" value="A"/>
          Option 1</label></td>
    </tr>
    <tr>
      <td><label>
        <input type="checkbox" name="CheckboxGroup[]" value="B"/>
          Option 2</label></td>
	</tr>
	<tr>
	  <td><label>
	<input type="checkbox" name="CheckboxGroup[]" value="C"/>
          Option 3</label></td>
	</tr>
  </table>
<p><input type="submit" name="Finish" value="Finish"/></p>
</form>

The problem is that wordpress looking for the process.php into the wp-admin folder and not in my plugin folder. I tried using the whole directory but nothing changed. If i put my process.php into wp-admin folder everything works but i know this is not the solution. If anyone has any idea please guide me. Thank you. Here is the code from process.php

<?php
include_once("phpchartdir.php");

$temp = $_POST['CheckboxGroup'];

# Check which (if any) of the queries was selected

if(empty($temp))
{
    echo("You didn't select anything.");
}
else
{
	$N = count($temp);

    for($i=0; $i<$N; $i++)
	{
		if($temp[$i] == "A")
		{
			# SQL statement

			$SQL = "SELECT COUNT( post_id ) , poster_id, wp_users.user_login, wp_users.ID FROM wp_bb_posts, wp_users WHERE poster_id = wp_users.ID GROUP BY poster_id ORDER BY COUNT( post_id ) DESC LIMIT 10";

			# Connect to database and read the query result into arrays

			mysql_connect("localhost", "root", "0000");
			mysql_select_db("wordpress");

			$result = mysql_query($SQL);

			while($row = mysql_fetch_row($result))
			{
    			$counter[] = $row[0];
    			$user_login[] = $row[2];
			}

			# Print the query's graph

			# Create a PieChart object of size 360 x 300 pixels
			$c = new PieChart(360, 300);

			# Set the center of the pie at (180, 140) and the radius to 100 pixels
			$c->setPieSize(180, 140, 100);

			# Add a title to the pie chart
			$c->addTitle("Pie");

			# Set the pie data and the pie labels
			$c->setData($counter, $user_login);

			# Output the chart
			header("Content-type: image/png");
			print($c->makeChart2(PNG));
			#$c->makeChart(dirname(__FILE__) . "/aaa.png");

			unset($counter);
			unset($user_login);
		}
                else if($temp[$i] == "B")
                #and continues like that........