RSS FEED Reader suggestion wants

An RSS Feed Reader is a tool that you install on your computer, or an online service that you use to get news from one or more RSS Feeds.

Since you are saying that you want the latest posts to appear in the blog sidebar, I would assume that you would like to display items from the forum rss feed, into the blog sidebar.

Is that the case?

If is the case, then you would have to use either the Feeds.App Lite plugin which is shaped with movable type v5.x and whose templating structure is provided here:

http://www.movabletype.org/documentation/appendices/tags/feedentries.html

Or, for more advanced operations, you could use Tim Appnel's Feeds.App plugin from:
http://appnel.com/code/feeds-app

Kind Regards,
Mihai Bocsaru

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Movable Type Consulting
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Thank you. Download the Feeds app lite and copy to the plugin folder.
In template mane, click the 'Create a feed widget', return this error(I can find FeedsWidget/CMS.pm there):

failed loading package FeedsWidget::CMS for routine FeedsWidget::CMS::start: Can't locate FeedsWidget/CMS.pm in @INC (@INC contains: /usr/lib/cgi-bin/mtos5/plugins/WidgetManager/lib /usr/lib/cgi-bin/mtos5/plugins/WXRImporter/lib /usr/lib/cgi-bin/mtos5/plugins/MultiBlog/lib /usr/lib/cgi-bin/mtos5/plugins/Textile/lib /usr/lib/cgi-bin/mtos5/plugins/spamlookup/lib /usr/lib/cgi-bin/mtos5/plugins/zemanta/lib /usr/lib/cgi-bin/mtos5/plugins/TypePadAntiSpam/lib /usr/lib/cgi-bin/mtos5/plugins/StyleCatcher/lib /usr/lib/cgi-bin/mtos5/plugins/feeds-app-lite/lib /usr/lib/cgi-bin/mtos5/extlib /usr/lib/cgi-bin/mtos5/extlib lib /etc/perl /usr/local/lib/perl/5.10.1 /usr/local/share/perl/5.10.1 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.10 /usr/share/perl/5.10 /usr/local/lib/site_perl .)

What about trying out the Feeds.App plugin from Tim Appnel's Website?

Lovely, thank you!