This one is “for the records” and not anything I endorse any longer: if you are trying to quickly style something for IE only you can do:
#property: value; for all IE
_property: value; for all IE except IE 7
The above will address IE but are invisible to other, standard web browsers, such as Safari, Firefox etc. The underscore seems to be valid (i.e. will not invalidate on W3C check), but it is good practice to not intermingle hacks with your general CSS but to but it into conditional tags in the header or conditionally linked CSS file.
I used to be fan of “all in one place” for any hook but got tired of all the warnings Firefox puts up when using the * hack, and since I began using conditional styling life has become cleaner and hacks quite easy to manage.