Thanks, now I can ask my detailed questions.
1. What sand can I use? I am planning to use real plants in the tank. A friend here at work said he has a full bag of unused swimming pool filter sand. You know, those silicone (I think) sand that they use in that big tank thingy to filter/backwash etc the water.
Will this be ok?

Plants. What food do they need? Do I have to use real mud or can I just put them in the normal swimming pool sand that I want to use. I can get at the local petshop a bottle of water plant food drops for aquariums that you put a few drops of in on a monthly basis.

I am still in the planning phase before I start to buy stuff and put it through a cycle and then adding fish.
It is actually the little guy's Christmas present but my wife and I are more excited and enthusiastic about it.
It is going to be +- 20 to 25 liters thank. Not big because I live in a town house and don't really have space for one of those big suckers.