Hola maika52.
Yo le haría unos pocos cambios, entre ellos el uso de botones para poder deshabilitar mas facilmente. Quedaría asi:
Código PHP:
<html>
<head>
<!-- PRIMER PASO: Copiar dentro del tag HEAD -->
<SCRIPT LANGUAGE="JavaScript">
<!-- Original: Mike Canonigo (mike@canonigo.com) -->
<!-- Web Site: [url]http://www.munkeehead.com[/url] -->
<!-- Begin
NewImg = new Array (
"images/1.gif",
"images/2.gif",
"images/3.gif"
);
var ImgNum = 0;
var ImgLength = NewImg.length - 1;
//Time delay between Slides in milliseconds
var delay = 3000;
var lock = false;
var run;
function chgImg(direction) {
if (document.images) {
document.frm.prev.disabled = false;
document.frm.next.disabled = false;
ImgNum = ImgNum + direction;
if (ImgNum > ImgLength - 1) {
document.frm.next.disabled = true;
}
if (ImgNum == 0) {
document.frm.prev.disabled = true;
}
document.slideshow.src = NewImg[ImgNum];
}
}
function auto() {
if (lock == true) {
var ImgNum = 0;
document.frm.prev.disabled = true;
document.frm.next.disabled = false;
lock = false;
window.clearInterval(run);
}
else if (lock == false) {
document.frm.prev.disabled = true;
document.frm.next.disabled = true;
lock = true;
run = setInterval("chgImg(1)", delay);
}
}
// End -->
</script>
</head>
<body>
<!-- SEGUNDO PASO: Copiar dentro del tag BODY -->
<form name="frm">
<img src="images/1.gif" name="slideshow">
<table>
<tr>
<td align="right">
<input type="button" name="prev" value="Previous" onclick="chgImg(-1)" disabled></td>
<td align="center">
<input type="button" name="Auto" value="Auto/Stop" onclick="auto()"></td>
<td align="left">
<input type="button" name="next" value="Next" onclick="chgImg(1)"></td>
</tr>
</table>
</form>
</body>
</html>
Espero que te sirva.