DVD Kungfu not found. Globe Life not found. Scots Kilt not found.

One of my client sites has been getting a lot of hits like these lately:

http://www.example.com/?q=DVD+Kungfu
http://www.example.com/?q=Asia+Tours
http://www.example.com/?q=Texas+Laws

All of these are from the same IP. The frequency seems to vary, but is often as much as several per minute. I have tried blocking the IP, which solves the problem temporarily, but then it just starts back up again within a day or so, from a different IP.

This is the first time I've had to deal with this kind of spam, and I wanted to ask what modules or techniques are the best to handle this.

I have found lots of posts about comment spam, but am having trouble finding information about this particular problem.

Thanks,
Scott Nelson