formatting apache rewrite rule

Hello all,

I have dynamic pages that look like this.

/index.php?purl=text_variable_with_underscore_2355.html

What would be the rewrite rule to get them to look like this.

/text_variable_with_underscore_2355.html

There is no other page besides index.php for this site.

Thanks

please post 2-3 "real" urls