@ Coriolis
Pfew, taxes in The Netherlands, rocket science is easier. I'm not a tax expert, but I think I can answer your questions.
The taxes are paid in two ways. There are direct taxes (they are withheld from your pay, such as income tax) and indirect taxes. The latter often involves filling in a form and sending it to the Tax Agency. This insitution then checks if you should pay a certain tax and if your're unlucky, you'll recieve a bill within a few weeks.
There are dozens of different taxes, so we don't have one national tax. Also, not only the state levies taxes; the 12 provinces, the municipalities and the Water Boards (special governmental institutions which handle the water management and keep our feet dry) also levy taxes. The government levies taxes such as the income tax (2.5% for the lowest incomes, 52% for the highest), corporate tax and the very high withholding tax (used to pay all the national insurances). All of these taxes are withheld from your pay. The provinces mostly levy eco-taxes which apply mostly to polluting companies. The municipalities levy taxes to keep the cities and towns clean and healthy. Examples of these taxes are sewertax, parkingtax and a special tax which people who own a house have to pay. The Water Boards levy taxes to keep the system of dikes and pumps up to date (yes, dike-tax

)
Along with all these taxes, there are also special sales taxes (Value Added Tax, or BTW, as it is known here). This means that 19% of the price of a product or service goes to the state. Of products which are necessary, such as water, vegetables and bread, only 6% of the price goes towards the state. Also, some products, alcohol, tabacco, fuel and especially cars, have a special excise duty.
As for the local taxes, the fact that municipalities and provinces can levy taxes also means that they can decide how much should be paid. This means that the amount of tax that should be paid is different in every province and municipality.
My own situation is pretty relaxed. I don't have a real job (I work one month a restaurant, then I work in a call-center for a few months, etc) and I still live with my parents. This means that I don't have to pay a lot of taxes. I only pay the withholding tax when I'm paid by my temporary employer and whenever I recieve my student grant.
Now, why did I have to pay $750? Well, the amount of student grant I recieve is based on a lot of things. The income of my parents is one of them. The higher their income, the lower my student grant is. My mom's income increased in june '06 and the Tax Agency didn't notice this. I was given 'too much' money and now I have to pay it back.
Hope this clarifies everything a bit.