Browsers, do they treat a random query string as a different file?

If I set a far future expire header for this file (take note of the query string):

/css/getCSS.php?v=1284532156.css

Will it treat the entire URL (including the query string) as a single file and respect the expire deceleration, but request the next version of the file...

/css/getCSS.php?v=1284599999.css

...from the server as it won't have it in cache yet?

I'm not in a position where I can use .htaccess to mask / rewrite a file from /css/v156845156.css to /css/getCSS.php?v=v156845156.css and unsure whether including the unique file name in the query string will be sufficient to make the browser behave like any other, differently named files.