You can probably do it using tables. In tuxquote.php, modify the return command as follows:
tuxquote.php:
function tuxquote_build_format:
return "\n<div style='float: " . $align . "; width: " . $div_width . "; '>\n"
.$title_line
." <table border='0'><tr><td><img style='width:150px' src='".tuxquote_choose_image()."'></td>\n"
." <td><p style='text-align: center'>".tuxquote_choose_quote()."</p></td></tr></table>\n"
."</div>\n";