deny file types

Dear All:

We have a lot of traffic to our site and we're running out of Apache's
MaxClients (apache has a maximum number of connections, maxclients, and
we're
reaching it).
As around 80% of this connections are requesting static content, we
would like to use a different, smaller webserver to serve it.
The problem is that we don't have other machine to run it, so we're
going to assign another ip to the server run thttpd on the other ip.

Now: we've configured mathopd to run on the same server, with the same
document root, but we need to configure it to deny the request of any
file which is not one of: *gif, *jpg, *png.

How can we do that?

Thanks in advance

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