All major distros follow the FHS (http://www.pathname.com/fhs/pub/fhs-2.3.html
) when they do their packaging. This means they change the installation prefix for the installation from /usr/local to /usr and ensure that things like binaries and configuration files don't go into wacky and inconsistent locations. In short your squid config files will be in /etc/squid/ on any major Linux distro even if the squid people have them default to somewhere in /usr.
They wouldn't have made any changes to the config file though - its normal to have a 2500 line config file for squid (
) with almost everything commented. The only changes Mandriva might have made is if you run the internet sharing wizard after you installed it as that sets squid up as a transparent proxy.