For form input, you can provide default values or you can simply add a column with the current value:
<form action=script.php method=get>
<table align=center>
<tr valign=top><!-- Display current value separately -->
<td>Username:</td>
<td><?php print($name); ?></td>
<td><input name=username type=text /></td>
</tr>
<tr valign=top><!-- Display current value as default -->
<td>Homepage:</td>
<td> </td>
<td><input name=homepage type=text value="<?php print($homepage); ?>" /></td>
</tr>
<tr valign=top><!-- For a checkbox -->
<td>Hobbies:</td>
<td> </td>
<td>
<select name=hobbies size=3>
<option value=tv<?php if ($tv) print(' selected'); ?>>Watching TV</option>
<option value=php<?php if ($php) print(' selected'); ?>>Writing PHP</option>
<option value=surf<?php if ($surf) print(' selected'); ?>>Surfing the Net</option>
</select>
</td>
</tr>
</table>
</form>