Improving performance by using an additional static file server

Varnish Cache is great for this!

_{(source: mocsystems.com)}

You may find this article interesting.

I'd say the first thing to do is to just start with mod_expires to reduce static file requests, then perhaps add mod_deflate to lower bandwidth.

Only once you actually see serious load then start partitioning on to seperate servers.

Moving static requests to a different vserver on the same apache (probably using the same document root) should be a good first step at partitioning.