$wpdb->update won't write to database

Hi,

I’m mucking around writing my first plugin for WP, but I’m stuck with the $wpdb object.

The plugin creates a new table in the database, with the code I found in the Codex.

Anyway, heres the code

<?php
            global $wpdb;
        if($_POST['oscimp_hidden'] == 'Y') {
            $blogcat = $_POST['cat'];
            $imageurl =  $_POST['image_url'];
            $wpdb->update( 'wp_blogcathead', array( 'blogcat' => $blogcat, 'imageurl' => $imageurl ), array('%s', '%s'));

            ?>

            <div class="updated"><p><strong><?php _e('Options saved.' ); ?></strong></p></div>

<?php        } else {
            //Normal page display
        }
    ?>
<div class="wrap">
            <?php    echo "<h2>" . __( 'Blog Category Header Images', 'oscimp_trdom' ) . "</h2>"; ?>

            <form name="oscimp_form" method="post" action="<?php echo str_replace( '%7E', '~', $_SERVER['REQUEST_URI']); ?>">
                <input type="hidden" name="oscimp_hidden" value="Y">
                <p>Select category: <?php wp_dropdown_categories(); ?></p>
                <p>Image URL: <input type="text" name="image_url" size="20" value=""/></p>

                <p class="submit">
                <input type="submit" name="Submit" value="Click it!" />
                </p>
            </form>
            <table>

I don’t get an error, but it’s not writing the two variable values.

Anyone know what I’ve missed?

Thanks.

PS I know the code is messy 🙂