Hi there, you can add video to a sidebar by pasting the appropriate shortcode into a text widget. No upgrade is needed.
Here's an example for YouTube:
[youtube=http://www.youtube.com/watch?v=XXXXXXXX&w=200]
Just replace XXXXXXXX with your video ID and 200 with a width in pixels that fits nicely in your sidebar.
There are shortcodes for several other video services, including Vimeo, Flickr and Viddler:
http://en.support.wordpress.com/videos/
Here's how to add a text widget to a sidebar in case you haven't done it before:
http://en.support.wordpress.com/widgets/text-widget/
If you do want the VideoPress upgrade so you can upload video to your own site, you can also use the VideoPress shortcode inside a text widget to display a video in the sidebar. Here's an example:
[wpvideo XXXXXXXX w=200]
If you have any other questions, just let us know.