Add "From Field" to CSS3 Mega Drop Down Menu

I just purchased the CSS3 Mega Drop Down Menu from Pixelworkshop.

I noticed when I fill out the contact form, the “from field” is a generic label from my host provider. I’d like to add the user’s email that sent the email instead of this long label that my hosting company fills in automatically. I know this can be added in the “sendmail.php? script.

How much to add the php field? Ron