Block that shows nodes based on node type
There's currently 12,966 sites using the beta3 release of Views 7 (http://drupal.org/project/usage/views). I'd suggest that you install the module and try to produce what you're describing as I suspect it will work fine. A beta3 release suggests that the module is nearing a production release with no new functionality being added.

Be brave, adopt the new software rather than painting yourself in a corner by writing your own custom code.