Change:
SELECT * FROM tutorials WHERE category IN ('Drawing, Effects, Forum Signatures, General Design, Photo Effects, Special Effects, Text, Tips & Tricks, Web Design)

To:
SELECT * FROM tutorials WHERE category IN ('Drawing', 'Effects', 'Forum Signatures', 'General Design', 'Photo Effects', 'Special Effects', 'Text', 'Tips & Tricks', 'Web Design')


If we knew your table structures, there'd likely be a much easier SQL query that we could use. But the above should work from what you've provided so far.