I've two questions.
1) Which is the best plugin to insert a portfolio in my Wordpress 3.1 (!!!) site? I would insert a title, a description adn a photo for each project. If it is possible could be interesting to add to the projects some custom fields.
2) It is possible to insert loop of news (not posts) in the home-page, for example in the sidebar of a wordpress site? There is a plugin to realize these operation?
Take a look at [[LINK href="http://codecanyon.net/item/ts-display-portfolio-and-gallery-plugin/147000"]]this plugin[[/LINK]] as a way of adding a portfolio to your website.
I'm not entirely sure I understand what you mean by inserting a loop of news but think I understand...
Perhaps create a category for "news" posts and then once you've published some posts in here you can grab the RSS for this category (go to the page that shows all the posts for the category and then add /feed/rss/ onto the URL, then copy the whole url).
Then, you can use the "RSS" widget - add it to your sidebar and paste the URL you have just copied into the first field before filling in the rest of the preference depending on what you want.
all of these can be done with wp help.
2) take look to <strong>Usage example</strong>
1) use a post_title, post_cotnent for descriptions, and featured image for posrtfolio image.
you can use as blog as custom post types for this proposes.