is_category and subcategories

Hi,
I have a conditional (is_category()) running on the archive.php of a theme, so that it sets a certain variable for a certain category. my problem is that i want that to be set also if it’s a subcategory of that category.

I searched the forums, and all i came up with was this. the problem is that i don’t want to create a separate archive page just for the setting of 1 variable, it will add clutter, and make future editing harder.

Any suggestions?

Thanks in advance