I use conditional comments to hide IE6 specific styles and scripts from IE7 (and IE7 specific styles and scripts from other browsers), but sometimes you need a bit of logic or something to only run on IE6 and earlier. Conditional compilation is a pretty foolproof way to handle that.

function ie_function() {
/*@cc_on @*/
/*@if (@_jscript_version < 5.7)
do_ie_6_stuff()
/*@end @*/
}

the @cc_on block turns on conditional compile. Since it’s wrapped in a comment block every other browser just ignores it. The next line (@if (@_jscript_version < 5.7)) tests for the specific JScript version present in IE7. If it’s there, nothing else happens. Otherwise the code on the next line is run. Wicked. Flip the comparison operator to >= and you’ve got a foolproof test for IE7. Double wicked.