The last mod I did was my banner, which I changed several times, adding <center> and </center> html command where it goes, but I don't see any way that could extend itself to the post area, right?
Where did you enter that center tag? That is depricated btw and it shouldn''t be used. Anyway, your posts appear fine to me, left-aligned as it should.
P.s. A bit off topic, but I think it would be best, security-wise, if you upgraded your forum to the latest version.