You can't make things random with pure HTML... you need some type of scripting language like PHP/ASP. Javascript could do it as well but less efficiently. Where no PHP is allowed (it's not your site, like SEN's signatures), you'd need to use your server's htaccess to randomize the file that's being called when one specific file is called.
And yes, & should be in titles/alts... and basically everywhere else as well. But if you were concerned about standards... your code would look a little different, maybe something like this:
CODE
<p style="margin:0 auto 0 auto"><a href="http://www.totse.com/"><img src="http://www.totse.com/image/totsead1.gif" alt="& the Temple of the Screaming Electron" style="width:450;height:50;border:0px;vertical-align:bottom"><!-- 1-7 --></a></p>