It looks like the include_path setting is wrong. That shouldn't be the folder it is looking in. Unfortunately I don't know that much about configuring XAMPP, so I can't comment on the precise fix.
It does appear that it is a configuration issue... unless of course the confirm_cart.php page doesn't exist. I see you haven't included it in your post.
I could probably figure it out if I did a screen sharing session with you and could actively debug. If you want to sign up for a premier support ticket I could help and I wouldn't charge you if I couldn't fix it.