[web] Javascript form inputs

I'm not sure whether this is in the right forum or not but here goes anyway. Say I've got a form setup like the following:

<form action="index.php" name="list" method="post">
<input type="text" name="txt[]" value="" />
<input type="submit" name="submit" value="Submit" />
</form>

And I've got a piece of &#106avascript to add another input box each time a button is clicked (it's actually set up with divs and stuff but for simplicity's sake I'll just refer to the above one). The &#106avascript needs to be able to select the value of one of those input boxes. In firefox the following gives a syntax error: document.list.txt[].value (which is understandable) but this apparently has no value: document.list.txt[0].value. When I change the value of the input box so that it isn't empty I get the same results. There is a workaround involving names like txt_1 and looping through them. But I'd rather not do that because it creates extra code on the &#106avascript as well as the PHP side. I just want to know if there is a way of getting the value of an array of input boxes. Any help would be welcome. Thanks, Fyorl