You won't be able to use Arduino to store the logs; it just doesn't have enough capacity for something of this size.
You would need to interface it with a computer, perhaps a small laptop. You would then need it to communicate with that computer, possibly via Processing (http://processing.org/) which is a relative of Arduino. There are libraries for Arduino <-> Processing which will allow the two to communicate, but you are looking at extra work here. Processing will be able to write your data to a file which you can manually work on - or you can use Processing to represent this data in charts, etc.
So basically, you'll be aquiring the raw data via Arduino and pushing it into Processing, where it gets more complicated depending on how much work you want the software to do. Thankfully Processing is not that hard to program, actually I think its easier to program in Processing than in Arduino.
Unless someone else has an idea...