Try Linux Mint 9.0 and set it up for a dual boot arrangement. This lets you keep your XP/Win7 world completely untouched (gives you peace of mind, it does). Heck, you can run Linux Mint for months on end off a simple live CD startup instead of installing it, it is all the same stuff anyway.
Linux only requires 20-30 gigs of HD space, so you can afford to shrink your Windows partition by 20-30 gigs and then let the Linux live CD recognize the unused space as available and the live CD will do all the heavy lifting for you.
http://download.cnet.com/Easeus-Partition-Master-Home-Edition/3000-2248_4-108... is a free partition manager that can shrink your windows partition without losing any data or hurting anything -- very easy to use.
Linux is actually pretty boring ... Linux Mint is very much like XP and it just runs Firefox, Opera, Chrome etc just like Windows does, just without any exciting stuff like blue screens and forced cold boots and my favorite, the unannounced screen lock ups.
What is also missing is the every Tuesday invasion of Microsoft security patches of the week and the bi-monthly attack of the virus/trojan/root kit of the week. And there is no anti-spyware software and stuff running all the time eating up all your processor cycles and systems memory and then asking you to go update it every 2 days.
And there are no adwares -- none. Heck, I miss scraping my adwares every time I used the XP machine. And no having to go Systems Restore every other weekend either.
It's too durn boring, you don't even have to reboot it when you do take the occasional Linux update that you get politely notified is available.
Dull -- Your linux file system doesn't even fragment your files on your hard drive (no defragging needed, ever)
Boring