Thank you for hitting us up for support. Yes you can! (use HTML in your announcement list)
Just click until you see a check mark appear in the little "This is HTML" checkbox next to the submit button on the mail page. This will result in HTML tags in your message being interpreted as HTML for people whose mail clients have HTML capabilities. You should paste your HTML code directly into the textarea that says "Your message:".
Also, don't worry that some people on your list can't read HTML-formatted email! Your message is sent as a multi-part message. Those users with email clients that can't read HTML will get a plain text version!
If you have any other questions be sure to let us know,