Add Meta Keyword and Description on MovableType

Just use following script as below

<meta name="keywords" content="<mt:EntryTags glue=", "><$mt:TagName$></mt:EntryTags>" />
 <meta name="description" content="<$MTEntryBody words="30"$>" />

Please be carefully when you change your template file.

Follow me.
Login your Movabletype 4
Desing > Templates
Open Entry Template

<title><$mt:EntryTitle encode_html="1"$> - <$mt:BlogName encode_html="1"$></title>

Add the code after it.
Rebuild your entry archives.
It is one of the most basic Search Engine Optimize methods. It make your entry page more Search Engine friendly.