Replacing $string within an array

I am reading in a text file, using

file("myfile.txt");

and in this file I have a form, but instead of having the HTML I have text field for a text box, and cbox for an option box with a yes or no. I am then replacing all instances of "text field" with <INPUT TYPE="text" NAME="txtbox[]">. I have this page submitting to a page that is supposed to take the values submitted from the last page and replace all instances of "text field", in the text file, with the values submitted right now I am using

$formfile = file("$form_filename");
for($index = 0; $index < count($formfile); $index++)
{
$textbox = ereg_replace("text field", "<U>&npsb&npsb&npsb$txtbox[$index]&npsb&npsb&npsb</U>", $formfile[$index]);
}

but I want it to increase the array number evertime it replaces, so that all the information is correct, but as it is, it will replace all the text fields on one line with the same text. I hope I made this clear, if not post questions, and I will try and make it more clear possibly submitting more of my files.

Chris

[This message has been edited by Chris Pickett (edited June 28, 2000).]