You could use this script in the head section:
var keycodec = event.keyCode
var keycodec = e.which
if(keycodec=='13') // checks for ascii code for enter key
return false; // So IE does not submit form when you hit the enter key in a form field
Then have your textarea tag like this:
<TEXTAREA ROWS="10" COLS="40" NAME="txta" onKeyDown="return dofunc(event)"></TEXTAREA>
The onKeyDown event seems to work better for both IE and NS where as the onKeyPress acts differently for both browsers.