Override A Value= In An Input Tag?

I have the following input tags:

Code:

<input type="text" name="fname_search" value="First Name" onfocus="clrFirstName()" size ="10" />
<input type="text" name="lname_search" value="Last Name" onfocus="clrLastName()" size ="10" />

As can be seen, the input fields have First Name and Last Name as the default values. What I would like to do then, is as soon as the user clicks in the First Name or Last Name field, that the field would blank out and allow the entry of the field. My JS looks like:

Code:

function clrFirstName() {
document.fsearch.fname_search.value="";
}

[code]....

fsearch is the name of the form.When I click on the field, nothing happens.