By default, IE allows only two outstanding connections per hostname when talking to HTTP/1.1 servers or eight-ish outstanding connections total. Firefox has similar limits. Using up to four hostnames instead of one will give you more connections. (IP addresses don’t matter; the hostnames can all point to the same IP.)
That’s actually an HTTP 1.1 recommendation (section 8.1.4);
Clients that use persistent connections SHOULD limit the number of
simultaneous connections that they maintain to a given server. A
single-user client SHOULD NOT maintain more than 2 connections with
any server or proxy. A proxy SHOULD use up to 2*N connections to
another server or proxy, where N is the number of simultaneously
active users. These guidelines are intended to improve HTTP response
times and avoid congestion.
A minor nit: the approach recommended in “Optimizing Page Load Time” is;
Rather than loading all of your objects from http://static.example.com/, create four hostnames (e.g. static0.example.com, static1.example.com, static2.example.com, static3.example.com)
That may not be optimal solution though – if you’re using cookies with a domain like .mysite.com then clients will be sending cookies in their static content requests – that may miss the opportunity to have intermediary proxy servers cache for you, further distributing load / reducing network distances – described in Michael J. Radwin’s HTTP Caching & Cache-Busting for Content Publishers under “3. Cookie-free TLD for static content” (watch for speaker notes).
In other words, when you get to start worrying about this stuff, you probably want to think about registering a separate domain for static content, under which you can then employ subdomains to reduce page load time.