If you have a Google account and create albums in Picasaweb, you can insert them as slideshows in your blog, by turning the original embed code into the appropriate shortcode (for more on this, see The gigya shortcode: inserting Flash).
Click on an album, click “Link to this album”, click “Embed Slideshow”. Select options, copy code. It will look like this:
Turn it to this:
(That’s the easiest way to do it: actually some of the attributes inside the code are useless, but you needn’t bother with this.)
Paste into HTML post or page editor (or into a text widget for your sidebar). Dimensions can be freely changed.