I agree with druidelder. I taught myself HTML and all that jazz with frontpage. I quickly learned that using only IE for testing isn't acceptable. IE is WAY to forgiving with broken code. It will put in tags that it *thinks* you meant to put in. Coding like that will ingain bad habits, and will leave you with a rude awakening if you go into XHTML, XML,XSLT.
Test in other browsers (and platforms for that matter) like Netscape 7/Mozilla, as well as IE. You can forget about Netscape 4.7x and below unless you are a professional and your client requires that their pages work in older browsers. (as for Opera, I am a professional, and it has never been a concern for any of my clients or projects. Basically, if you code well, and it works in Mozilla and IE, it will probably work in Opera.)