not to cache some files...

Hi!

My question: I want to configure my squid server in order to get a file on
a server at the first visit, and then to get the cache copy only if it's
the same file than on the server and if not, I want to get the file on the
server.

I explain: I've got a problem because when i want to download an
executable on a Web site (at the first time it's ok) but then if the
executable version change i still download the cache file which is the old
version !!!! Which is BAD.

I've tried to change the squid.conf with :
refresh_pattern ^ftp: 0 20% 10080 override-lastmod
refresh_pattern ^gopher: 0 0% 1440 override-lastmod
refresh_pattern . 0 20% 4320 override-lastmod

But it doesn't work.
I've tried this which is not what i want, but it doesn't work anymore:

acl QUERY urlpath_regex -i cgi-bin \*.exe EXE exe \?
no_cache deny QUERY

I've probably forgot some thing??...

Thanks for your answers

-- 
Guillaume