If you use an RSS aggregator (like my CG-FeedRead) to do the work, you could get the most recent post, or comment, or comment on a particular post, or anything else you can pick up via RSS. ??
RSS has another advantage: so long as you are using a caching aggregator (CGFR does, and I think most of the decent ones do), then it is only an html include on pageload while it is cached. When the timer expires and it needs to refresh, it polls the WP site for the RSS, and gets what it needs. In any case, you never directly include WP in your page, and you certainly never directly hit a SQL database to look something up.
Just IMHO, a much better way to approach the problem. ??
-d