If your machine has Windows already, installed and you have documents, spreadsheets, pictures, or music files that you wish to keep, now would be a good time to back those things up, either on diskette or burned to a CD-ROM. Even if you plan on preserving your Windows installation for a dual-boot system, it's always prudent to have a good backup if you are going to be doing major work on your hard disk. You might also want to take advantage of all the hard work that was done in pre-installing Windows and make notes on all the hardware in your machine the type of network and video cards and anything else you can think of. You do that by clicking the Start button, selecting Settings, Control Panel, then double-clicking the System icon. Now walk through the hardware profiles and take some notes. Odds are you won't need it at all, but you can never have too much information.
The average Linux installation takes about 30-60 minutes, although I have seen it take as little as 5 minutes on a really fast system. That's a fully network-ready, configured, all-set-to-work machine with no rebooting every few minutes to load another driver. It doesn't get much easier than this.
That said, unless you are feeling particularly adventurous, I would highly recommend that you read through this chapter once before actually starting.