blog spam

I have been receiving a lot of spam on my blog. I have locked it down ao that I have to approve comments, and add the ip addresses daily to the block list, but they are still coming in. I added the robots file to the site with this : User-agent: *
Allow: /

User-agent: Googlebot
Disallow: /

Would the disallow effect my ratings?? also any other ideas without paying a monthly fee. So far I have to add IP’s to block list daily…. It is such a pain.