Usergroup based on IP address?

[JPnyc]

I'm sure every forum admin has the same problem with spam that we do. What I would like to do, and I need some guidance as to the best approach, is to have a list of partial IPs (just the 1st group of numbers would be enough to test for), which would place the new registrant in "premoderated" usergroup I have added to the forums.

I have scripting/programming experience, but unfortunately, not PHP and not with respect to vbulletin. I can look up the PHP methods easily enough but I need some advice regarding how to apply it to the plugin system.

Since this is for new signups only, where would you hook it in the plugins? Would you use an external file for the list, or would you hard code the partial IPs right into the function test?

What I have discovered is, 99.99% of all spam we get comes from India, Nigeria, Russia, and China. There's a trickle from other countries, but those 4 account for the bulk of it. Rather than ban whole ISPs and nations, I thought this approach would be ideal.