Ok, so I have decided to give Linux a try.

I'm getting a mSATA SSD for my X220 as a second disk drive and I'm going to put Linux on it. I'm going to keep Windows 7 as my main OS on my main drive. I'm a graduate student, and form time to time have to deal with programs just don't work well or at all on Windows. The first question is, what Linus distribution should I try? Ubuntu? That seems to be a very popular choice. I really don't have much experience with Linux, so I am looking for one that is easy to maintain, install, and update. The second question is, is there anything that I should be careful when installing the Linux OS (whatever distribution), so that it won't intervene with my Windows OS?

It should install fine, but will control the MBR. If you remove the mSATA later, it'll probably mess up the boot process. I'm sure there's a way to fix it, but I haven't got that far yet. I run Ubuntu on my R60e and it works quite well. I did have Mint on there, but it had a few issues.

Since you will have 2 separate drives, it is possible to install Linux on your new mSATA SSD without touching anything on your main 2.5 inch HDD. To prevent any possibility of screwing up, simply put the mSATA SSD in, remove the 2.5 inch HDD, and install Linux as if it's your only OS. When the installation is complete, put your HDD back. You can then choose which OS to boot by pressing F12 at the BIOS splash screen and pick your boot device. (It's also possible to chainload Linux from the Windows boot menu.)

As for which distribution... I don't like newer versions of Ubuntu because of their new Unity desktop. Consider Kubuntu (Ubuntu with KDE desktop), or maybe Fedora.