I also noticed a typo in the url media-upload.php?type=image&&TB_iframe=1
. Maybe this is the problem.
Also a working example:
jQuery( 'input[id^=my_field]' ).live( 'click', function($) {
formfield = $( 'input[id^=my_image]', $(this).closest('.widget') ).attr( 'name' );
tb_show( '', 'media-upload.php?type=image&TB_iframe=1' );
return false;
} );