1) Does modules used with/written for apache 1.3 work with apache 2.0 ?
>> no, you need to recompile these modules for apache-2.0.
2) Does modules for apache 2.0 work with apache 1.3 ?
>> for apache itself, the modules contained by 1.3 should also available for 2.0 and 2.2, for issues about the unknown modules, please mention us
3) What does it mean when something is proxied from a front-end server to a back-end server?
>> when you are using a proxy server between your customer and the REAL web server, the arch is mostly like this:
Customer Browser ----> Proxy Server(squid) ----> Real Servers(apache,IIS)
The proxy server has a local storage for the content from real servers. when proxy server find user requested content is locally available, he will not sent request to the backend real server. this is the cached content, can also call it proxied.