Yes...you can define multiple dynamic sidebars in your theme. Then you can use some PHP in your theme so that WordPress can determine what kind of page it's delivering, and tell it to deliver a different sidebar based on that.
A lot of themes come with just one dynamic sidebar registered. To add more, you need to be comfortable editing your functions.php file in your theme to register it.
This tutorial might get you started:
http://www.quickonlinetips.com/archi...press-widgets/
The concept works in WP 2.5 too.
Great question! Looking for the answer got me thinking. I think I'm going to create multiple sidebars for my site. I don't want all my categories and monthly archive widgets to show up on post pages (because they make the page unbearably long).
= )
--David