I have an external hard drive connected to my Macbook Pro that I always leave on. When I use spotlight to search for something, it always searches this drive. I don't want it to do this because usually the drive is in standby mode, so it takes a while to power up when I use spotlight to find something, and usually what I'm trying to find isn't on that hard drive. How can I prevent spotlight from searching this drive?
System Prefs --> Spotlight --> Privacy.
Add the drive(s) you want to exclude.
For a scripting approach try this: Disabling Spotlight in OS X Leopard for the removable drives
Should work for Snow Leopard too.
Assuming you don't want Spotlight to index the drive either, create a file,
on the root of the drive. It will no longer get indexed, and, no index, no search. From this tip from Mac OS-X Hints.