Can my parent legally claim me if I'm over 18 and not a student but live in their house?

Yes, if you are a qualifyig dependent, which would be the case if you have gross income of less than $3,400 for the year and your parents provide over 50% of your financial support. See the following for details:
Publication 501 (2007), Exemptions, Standard Deduction, and Filing Information (http://www.irs.gov/publications/p501/ar02.html#d0e3763)

Agreed!