CDM  I had the same problem (macbook pro running leopard; internet cleanup 5.0). I booted from a clone to access the hard drive (alternatively you could access your HD in target mode from another mac). I then deleted everything I could find associated with internet cleanup. I deleted a bunch of .plist files, but I think the critical files to delete were netblockade.kext and/or netspywareblocker.kext (I might be misremembering that filename, but search for .kext files and you'll see the ones I mean). After that my machine booted; I downloaded the IC software again and chose the uninstall option. Things now seem to be back to normal.

Now to ask for my money back.  
(Version 5.0)