Internet Explorer 7
html>body #center { *float: none; }

Internet Explorer 6
* html div#block { css rules }

Safari
@media screen and (-webkit-min-device-pixel-ratio:0) {
/* Safari 3.0 and Opera 9 rules here */
}

Firefox
#hackme, x:-moz-any-link {styles for Firefox 2.0 here}
#hackme, x:-moz-any-link, x:default {restore styles for Firefox 3.0 and newer}

Somtimes you just gotta...

As Tim Gunn says, make it work.