<p>Here's the information you need on cross-registration. <a href="http://web.mit.edu/shass/undergraduate/programs/cross-reg.shtml%5B/url%5D">http://web.mit.edu/shass/undergraduate/programs/cross-reg.shtml</a></p>
<p>The answer to your question is no: "The Cross-Registration program does not include classes at the Harvard Extension School or Harvard Summer school."</p>