Populating craft database from non-craft data
Brad is absolutely correct. Better off trying for an existing plugin (we have one in the works over here for very robust Wordpress migrating!!!), but here are a few steps to get you started:

Move the non-craft database tables over to a staging server with your craft tables, and rename them with a craft_ prefix (or whatever you have set as your prefix in config). 
Query for the entries

$query = craft()-&gt;db-&gt;createCommand()
-&gt;select('*')
-&gt;from('your-non-craft-post-table')
-&gt;where('any conditions')
-&gt;queryAll();


Loop through the query results, creating new Entry Models and assigning columns to your fields.

//Go through each $query result
foreach($query as $old_entry){
    $entry = new EntryModel();
    $entry-&gt;sectionId = your_craft_section_id;
    $entry-&gt;authorId = your_craft_user_id;
    $entry-&gt;postDate = $old_entry['old_post_date_column'];
    $entry-&gt;enabled = true;

    //This is the fun part - mapping content to your custom fields
    $entry-&gt;getContent()-&gt;title = $old_entry['old_title_column'];
    $entry-&gt;getContent()-&gt;yourCustomFieldHandle = $old_entry['column_to_map_to_custom_field'];

    //Use the Entries service to save the new entry
    $success = craft()-&gt;entries-&gt;saveEntry($entry);
}


Obviously there is more to it than that...mapping user accounts, categories, tags, assets, etc. But hopefully this will help you get started!