WP_Query() with Tags – possible?

Hey all, I am working on a rather customized theme and am integrating a “results count” that displays the number of items returned when viewing a category, tag or search page.

Category and search are all set using:
new WP_Query(“cat=XX”);
or
new WP_Query(“s=XX”);
respectively.

However, when I use what I assumed would work for tags pages:
new WP_Query(tag=XX);
it doesn’t return anything.

Does WP_Query not work the same way for tags as it does for categories and search results?

Any help is much appreciated.
DBD