Too Much of a Good Thing: The Pitfalls of Simplification
While it's good to eliminate unneeded services, applications, and other PC clutter, going too far can turn a PC that's merely annoying into a nonfunctioning one. If you run Windows XP, the System Restore tool can and will save your behind (and your system) if you ever cross the line that divides PC simplification from a PC lobotomy.
In general, if you're not sure whether uninstalling or disabling a program or service is a good idea, leave it be. Google is a great way to find out what a particular program is--just search for the file name. Be certain you know what a program or service does before you disable it, lest you turn off something Windows needs to boot.
To prepare for that possibility, make a bootable Windows XP emergency recovery CD (instructions here) before you start simplifying. Once you make the CD, test it, then put it somewhere safe and pray you'll never have to use it.
You're better off disabling those things you know are unnecessary, and then monitoring the PC for a day, just to make sure you haven't broken something. Always proceed with your simplification carefully, disabling one service or program at a time, and then rebooting to see if its absence causes a problem on startup.
If all is well, create a new restore point using Windows XP's System Restore tool, which takes snapshots of your system configuration and can restore a botched simplification effort with a few mouse clicks. Creating a restore point with this tool is easy: Choose Start, All Programs (or Programs), Accessories, System Tools, System Restore, select Create a restore point, click Next, enter a description of the restore point (such as 'right before starting simplification'), and then click Create.
System Restore also lets you create a restore point before you install new software, allowing you to back out of any unwanted changes the new program makes to your system. Thanks to System Restore and the emergency recovery CD, you can feel relatively free to simplify without much risk of turning your PC into a paperweight.