html code probelms on pages

I was wondering if there are any solutions to the problem that what I put into the editor, whether it’s straight from the editor in WordPress or pasting in html, doesn’t output the correct way on the site itself.

I’ve been battling with page content not coming out the way I designed it in the editor. Is this a defect of using artisteer themes?

I know the CSS overrides but I don’t think the CSS is causing all of that.
Does this happen in all themes? is this an issue with WordPress?

Rick