Howto Point To A Textbox?

I just wondered how I can refer to the following two
textboxes in this form:

<FORM action="FormWrite.php" method="post" name="submitForm">
<INPUT NAME="inputValues[etunimi]" SIZE=40>
<INPUT NAME="inputValues[sukunimi]" SIZE=40>
<INPUT TYPE="button" onclick="javacscript:sendForm();"
VALUE="Lähetä">
</FORM>


the reason the [] signs are in the name is to get all the textboxes values
in one variable
when using a php script.

- But how can I refer to it with javascript? For example; I tried

alert(document.submitForm.inputValues[etunimi].value);