There's a method of Applet that retrieves a parameter. And you could use JSP or PHP or similar to write those params. So the user has a form, hits submit and gets sent to a page where PHP writes those values into params.
At it's simplest:
file1.htm:
Code:
...
<form method="get" action="file2.php">
<input type="text" name="box" />
<input type="submit" value="Hit me!" />
</form>
...
file2.php:
Code:
...
<applet code="MyApplet.class" width="200" height="100">
<param name="box" value="<?php echo $HTTP_GET_VARS[box]; ?>" />
</applet>
...
Of course this requires a web server where PHP can run.