The only other question remaining then is whether your computer and amp have the same size jack. If so, then all you'll need is the appropriate sized Y cable. If not, then you'll need to add an adapter to one side to make it work.
Don't forget also that you're almost guaranteed to need a couple of extension cables so that you have enough reach to plug both your computer and amp in... that Y cable may be too small to reach both your computer and amp, but check and see how much length you're going to need... you might be able to get a longer Y cable that will reach.
Write it out on paper and imagine yourself plugging in before you go to the store... I hate getting home only to realize I'm missing one key cable or adapter! :)