Sort of order form.

Hello,

I'm looking for a form, with one field, where you type a number in.
And then (in ajax i think that is, but could aswell be just js, you see that number multiplied by x appear somewhere in the page, without submitting the form.

Can someone link me to a tutorial or something please?

The only order for I've been able to find was http://javascript.internet.com/forms/order-form.html
And the only thing that it has wich I'm looking for is that it shouws the total amount of money.


Thanks!

/edit:
I also found this, but it's very complicated.
If i try to cut out parts it doesn't work, this one has to many options.