dead thread?
There are probably lot's of better articles on the intarwebs that discuss this apple spell thingy that troubles some people. I did however notice the contraindicated suggestion and thought best to donate a few moments of my time.
Apple spell is a great tool:
http://www.apple.com/pro/tips/spellcheck.html
I couldn't possibly imagine why anyone would want to turn it off, unless perhaps you are the greatest speller in the world. If you are concerned about memory usage, consider that apple spell uses approximately the same amount of memory as
cron.
However, if you absolutely needed it gone and gone forever never to return again then locate and delete the file AppleSpell.service (in 10.6 it is locate in /System/Library/Services) This may generate some errors as the launchd attempts to load the service.
Perhaps the most correct approach would be to use a program like lingon that would allow you to easily edit the .conf files. Though I suppose if you're brave enough you could just find them and edit them yourself. Probably more trouble then it's worth, but if you're gonna do it anyway, ensure you've got a good backup before editing any system files.