I've always been a Windows fan, and I love XP by far.
I'm getting bored with Windows, and after browsing around, Ubuntu seems pretty promising. I have a few questions.
Do you recommend it?
If so, should I buy an external hard drive and run it from there?
If you want to run a server, or are interested in developing a c/c++ app, or support free software as defined by fsf, or are trying to get a job as a sys admin, or just want to be part of some happening geek culture, then go ahead. Otherwise, I'd just stick with XP.
I would recommend it as a basic system like email, youtube, websites, personal finance and officework. If you want to use it for a more complicated system, you'll need access to a guru that can help you. If you just want to play around with it, you should get another HD and install it there.
Ubuntu is designed to be user friendly and is pretty easy going as far as "need guru" goes. I'd suggest the people suggesting you DO need a high degree of skill aren't running Ubuntu.
Download the livecd/dvd image from the nearest mirror and see if it'll fire up without incident on your machine. After that you can either continue and install it (dual-booting is the default) or decide it's not for you and shut the machine down, remove the disk and there's Windows again.