User-agent: Googlebot
Disallow: /_forum/*?action
Disallow: /_forum/*sort=
Disallow: /_forum/*msg

User-agent: Slurp
Disallow: /_forum/*?action
Disallow: /_forum/*sort=
Disallow: /_forum/*msg

User-agent: * 

Disallow: /_forum/index.php?action