That was how I learned, by setting it up as a dual boot. Linux is a good choice for a secondary OS. Ubuntu is the main one, followed by Mint, which happens to be partially based upon Ubuntu.
Mint 10 is the most current version, but 9 is LTS (Long Term Support, 3 years), while 10 is one of the 6 month releases. I prefer the LTS ones, you don't need to constantly upgrade.
Linux dual boots well with Windows, but if one has the extra drives, it would be better to install it alone, if it's on the same drive, then your bootloader would be GRUB, should you remove Linux, you'd have to do a repair install of Windows to fix the bootloader.
I haven't decided if I'm going to dual boot on my notebook that's arriving tomorrow, for now, I won't. If Windows 8 is released as a beta, I may.
I'm still half way tempted to try installing XP Pro 64 bit on here, it will no longer be my main computer. But I know it will be some work involved, however it can be done. If the OEM's can downgrade new computers, then drivers are available.
Plus, many of the critical parts in mine are outdated anyway (surplus parts from previous models), there's XP drivers for most everything. If I can only get it to boot, I'm sure that I can make it work. Whether I use it much makes no difference, it's a time killer to me.
Cat