Controlling Arduino with computer.

I'm guessing that this is something that has been done a lot. And I should be able to find many tutorials. But my Googling skills have failed me so I am coming here.

I have a simple physics project for school where I need to build a spring launcher. It is really simple. But I felt like going completely overboard and making it completely controlled with an Arduino. I plan to have the equations in the code and in the program I create I will simply have to enter in the details of the launch and the Arduino will automatically adjust the the tension on the spring as well as the height of the launcher. Hopefully that makes sense if not, not a big deal.

From what I have read so far; in order to control my Arduino via my computer I have to write a program using a language that allows serial access. Does that make sense? Such as C++? I have hardly any experience in coding such a thing. So I was wondering If someone could point me in the general direction of a tutorial of sorts specifically for people like me. Who only need to create a program for Arduino use.

Again, I hope that that all made sense. If there is an easier way for a n00b like me to approach this, it would be greatly appreciated.

I have to write a program using a language that allows serial access. Does that make sense?

Yes

Such as C++

Yes or practically any other language you like.

Processing is free and is often used to feed stuff into an arduino.

See section 4 of this page
http://arduino.cc/en/Tutorial/HomePage

Alternatively, i've found python with pyserial module to be extremly convenient and simple to hack around with... i've done decoding if ir signals, sending graphic primitives and bitmaps to arduino etc this way