Tech site ZDNet walks through how to trim the bloat from a fresh install of iTunes on a Windows PC.
The Windows version of iTunes 8 is a 64MB download. (For the sake of comparison, Windows Media Player 11 for Windows XP is just over 24 MB.) The full iTunes 8 installation takes up nearly 200MB of space on a Windows PC. As it turns out, the iTunes installer has been bulking up for the past year or two. Don't be fooled by the filename: iTunes8Setup.exe includes much more than the iTunes client.
The author explains that the iTunes 8 setup installs several drivers, system services, and at least one add-on that are completely unnecessary to the operation of iTunes on your computer. As a workaround, the article details how to extract individual installers from the iTunes setup client so you can install only what you need and want on your computer. iTunes may still take up more than its share of system resources compared to other popular media player alternatives, but at least this way you have a little more control over what programs it installs to your hard drive.