How do I validate my PHP form using the following code?

[Dannae]

This is the code I'm using, but it is specifically for drop-downs. I need to validate text and textarea too, but I'm not sure how to modify the code in order to do this. Would anyone know how to do this? Or point me to a page that explains the different options? I'm having issue finding this information. (Self-teaching myself...) THANK YOU FOR ANY HELP YOU CAN PROVIDE!

<!--
function validateForm(){
if(document.myform.day.selectedIndex==0)
{
alert("Please enter the start day.");
document.myform.day.focus();
return false;
}
return true;
}
//-->

*The IF line should look like this: if(document.myform.day.selectedIndex==0)
**Yahoo keeps cutting it off.