There's a very detailed, Terminal-intensive and (imho) somewhat just plain crazy and risky hack over at Mac OS X Hints that shows you how to eradicate Spotlight from Tiger. However, MacFixIt offers a simpler solution for turning off Spotlight if you just don't happen to like it very much.
To do this, launch your Terminal (located in /Applications/Utilities/) and type the following:
sudo pico /etc/hostconfig
This will open up your hostconfig file, which tells OS X what processes to launch at startup. Scroll down the hostconfig file and find the line that reads
SPOTLIGHT=-YES- and change it to
SPOTLIGHT=-NO-. Close and save the file. If you don't know how to use pico, type
man pico to read over it's man pages first. If you want to remove Spotlight from the menu bar, remove the file "Search.bundle" from the folder /System/Library/CoreServices, but keep it around somewhere in case you change your mind. When you reboot the computer Spotlight will not load.
If you ever want to re-enable Spotlight just go back through these steps and change NO back to YES and put "Search.bundle" back where it belongs.
Why would anyone want to remove Spotlight? According to MacFixIt, "We continue to cover an issue where Mac OS X 10.4's Spotlight function consumes inordinate amounts of processor time, resulting in slower overall system performance or seemingly complete systems stalls."