how to Connect wireless access point to wireless router

Hello

i would like to make network at my home between 2 computer beside mobile N95 to receive internet

actually now i creat local home network between my desktop and my laptop and N95

and this is its arrangement
I have Grid antenna connect by cable to wireless adapter in my desktop
from the desktop i have ethernet cable connect it to access point from which i receive internet to my laptop and N95

in this case my desktop should work every time i want to use the internet
what i want to do is to overcome this problem by make:

an access point work as client and receive the wireless signal from the provider and then use the ethernet cable connect it directly to router wireless without computer

how can i do that
if any one can help and how to configure both the ap client and router
my ISP is through PPPOE over wireless

can any help me please in setting up what i want as in the pic