build an order form with javascript

I ‘m complete new with javascript, but I’m used to php.
I would like to write my first javascript and need some hints.

This is the form:

total1=quantity1*10
total2=quantity1*15
total3=quantity1*20
total=total1+total2+total3

[QUOTE]

<form>
<input type=”text” name=”quantity1″ value=”” size=”5″ />
item1 for 10$
makes
<input type=”text” name=”total1″ value=”” size=”5″ />
<p>
<input type=”text” name=”quantity2″ value=”” size=”5″ />
item2 for 15$ makes
<input type=”text” name=”total2″ value=”” size=”5″/>
</p>
<p>
<input type=”text” name=”quantity3″ value=”” size=”5″ />
item3 for 20$ makes
<input type=”text” name=”total3″ value=”” size=”5″ />
</p>
<p>Total
<input type=”text” name=”total” value=”” size=”5″ />
</p>
</form>

[/QUOTE]

On the total1, total2, total3 and total textarea the multiplication should be print (echo) when a quantity is entered. Also the total should be displayed. Can you give me an hint?

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