http://www.systemrequirementslab.com
Have your friend go to that website and test the league of legends requirements, it will give him recommendations on what to upgrade.
Since no one has really answered the question for you.. its not as portable as the 13", but I still take mine with me without any problems. Its very light and relatively thin, I would recommend it.
Is the file your downloading actually finishing all the way?
Go to the Disk Utility, and select "verify disk" on your macintosh partition, and let it repair if necessary. Afterwards select "verify disk permissions" if repairing the disk doesn't correct the issue.
If crucial said your max is 4Gb, then it's 4Gb the site is usually pretty accurate. If 4Gb is you max then your computer will only be able to handle 2Gb per slot given your Pc only has two slots.
This just goes to show if you plan on gaming for a long stretch of time, or sit for a long amount of time it's a good idea to take a 5 minute break every now and then and get a good stretch and let the blood flow.
It's not your GFX card could possibly be ram though.. Since you wiped it I'm assuming you didn't use the recovery partition.. or did you? If you did you should still have the Dell Diagnostic utility.. Which you can access by pressing F12 when you first turn the computer on and see the DELL...
It looks like .rar files are associated with the wrong program.. /facepalm
Right click one of the files select "open with" find winrar and start the process over.
Sappire is a decent brand, I haven't heard anything too bad about them. It doesn't have a minimum wattage listed but I would suggest a 350w-400w for this card, as for games I'm not entirely which ones specifically it can play, but I'm sure it can play alot of the main stream games on a decent...