Found this earlier this morning. If you need to dump you DNS cache, the process has changed from 10.4 to 10.5

macosxhints.com - 10.5: Flush DNS cache:

“I primarily work with web servers, and I use lookupd -flushcache all of the time to clear my DNS cache.

This morning was moving some websites around using my newly-upgraded Mac, and I went to flush my DNS cache with lookupd and I got a command not found error. It seems that lookupd has been removed in 10.5 and replaced with dscacheutil.

So now I can flush my DNS cache with dscacheutil -flushcache.”

(Via Mac OS X Hints.)