Add tinyMCE editor in magento custom module

If we have created a custom module using Magento Module creator means, it will not contain 'wysiwyg(tinyMCE)' editor feature.
We can add the 'wysiwyg' editor in custom module within 2 steps.
Step 1:
Add the following code in /controllers/Adminhtml/BlogController.php under the line $this->getLayout()->getBlock('head')->setCanLoadExtJs(true).

if (Mage::getSingleton('cms/wysiwyg_config')->isEnabled()) {
 $this->getLayout()->getBlock('head')->setCanLoadTinyMce(true);
}

Step 2:Add the following code in /Block/Adminhtml/Blog/Edit/Tab/Form.php file, within your field declaration.

'config'      => Mage::getSingleton('cms/wysiwyg_config')->getConfig(),

Now, it will look like this

$fieldset->addField('post_content', 'editor', array(
  'name'      => 'post_content',
  'label'     => Mage::helper('blog')->__('Content'),
  'title'     => Mage::helper('blog')->__('Content'),
  'style'     => 'width:900px; height:500px;',
   'config'      => Mage::getSingleton('cms/wysiwyg_config')->getConfig(), 
  'wysiwyg'   => true,
  'required'  => true,
));

That's it! We have added tinyMCE editor in our magento custom module:)

Note: Field name should not be 'content' if you keep your field as 'content'(which is already available), editor will be shown all over the admin content block. So give some other name for content filed.