Ignore the silly answers. Ubuntu is a fantastic operating system. It's likely it will run better on your old machine than any Windows OS will.
Don't be afraid by the subtle differences and the "Terminal" which you will be told to use a lot. I use Ubuntu 9.04 and love it. It installs easy and quickly.
Give it a go but expect things to be different. Get to know the Synaptic package manager and the Add/Remove programs. Basically, you can say goodbye to googling for software, with synaptic you just put in what you need and it gets it for you and installs it for you. Well, most of the time. Though if you install Ubuntu 9.10, the latest one, you won't get these as they've been replaced by an all in one package manager.
I love Ubuntu and have tried various Linux flavours, some are good in their own way but Ubuntu is by far the best for the casual user. The only draw back is it doesn't have as many games as Windows, though that's not really the fault of Linux, it's more the games companies going for the more popular platform.
Give it a go, I think you will be pleasantly surprised.
Also Ubuntu has massive community support online, they have a massive forum where your questions are answered. You won't get people popping up with pointless posts because you of a typo. Good luck and feel free to PM me if you need any help.