Here's a useful little module I didn't know even existed, but it appears to have been added to the Microsoft download site in the past couple of days. It allows for bit rate throttling of common, supported, media files when served by IIS 7.0. IIS first sends the first twenty or so seconds of data at the fastest possible rate, and then streams the rest slowly.

Full information on configuring this module is available on the website. You can download the module from the Microsoft download site for x86 and x64.