In general, you should always have a mod rewrite to define the standard URL, either domain.com or
www.domain.com. Example: You want
www.domain.com, so you do a rewrite for domain.com, domain.com/index.html and
www.domain.com/index.html (or /index.php, whatever you index page's extension is) to automatically change to
www.domain.com or you could end up with 4 pages indexed, all with different PR and duplicate content ! Just one idiot linking to domain.com/index.html could (with a little bad luck) ruin your SE rankings, even if you have 1000 incoming links to
www.domain.com
How is your domain indexed ? If it's (
www.)domain.com/index.html, you'll temporarily face a drop of your PR and ranking, but they will recover over 3-6 months, if it's just (
www.)domain.com, there will be no (temporary) interruption in your SE traffic.