Yeah, strip out all HTML code. But first, email google with the full content of the entry - including the specific URLs for the ads - because whoever put that in is making money off of it, and my reading of the Terms of Service for Google ads would indicate that it's in violation. Report it to Google, and let them cut the jerk's income. (he's probably done it on other sites, too.)
*edit* I have submitted a report to Google - still send your own report, but here's the body of the message that I gave them, minus the URLs I specifically don't want to link to:
One of your customers is taking advantage of the poor input-filtering of certain shoutbox code to place iframes on other people's sites, which display and redirect to his own page. This technique is used with the aim of displaying his google ads on sites over which he has no legal or administrative authority. My reading of your Terms of Service (a quick scan reveals from section 13 "Representations and Warranties. You represent and warrant that ... (b) You are the owner of each Site or that You are legally authorized to act on behalf of the owner of such Site(s) for the purposes of this Agreement and the Program;") indicates that this practice is not permitted; thus I wish to inform you of its use in this situation.
The redirect forces the user away from their desired website and onto (removed to avoid autolink)
A URL from a Google ad on that page is (removed to avoid autolink)
I have noticed this on a site maintained by an acquaintance of mine - you can find the particular page at
http://manga.silver-essence.net/updates.php
I have advised her also to report this, as it is her site which was, essentially, defaced by this tactic.
I understand that Google is trying to set itself apart from the bulk of the "spam-for-cash" advertisers, but such behavior as this person is illustrating seems to go against the spirit of what you are trying to accomplish. I feel confident that this matter will be dealt with in a swift and appropriate manner.
*/edit*