I don't think it has anything to do with your character set. What you're using (iso-889-1) is pretty standard.
It's really your DOCTYPE that stands up and calls out what standards *you* are saying that you're following. Regarding DOCTYPE, I'd suggest using this intead of the HTML 4.0 one you're using now:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
Now, about those errors...
- topmargin is/was an IE-only attribute and is deprecated in favor of using css to control margins.
- background is also deprecated and the image should be spec'd in css.
- bordercolordarks, bordercolorlights only work in IE and Microsoft even suggest you don't use them any more.
- form: this one may have more to do with how you're using the form tag but I'd have to see your page to be sure.
A guide to which tags have been deprecated is
here.