FPS Help

I have mw2 mp game
but I'm having issues running the game at the moment and I will talk about it in another thread

but anyway
I have a really really really bad pc
take a look at the specs and you will know

my specs
CPU: Intel Pentium Duo Core
CPU SPEED: 3.00 GHz
GPU:Intel G41 Express Chipset
RAM:4 GB

I'm talking about the fullbright command bec it seems that my pc is producing an amazing amount of fps when fullbright on

Example:
in cod4 there is a map called Overgrown,it is the biggest map in cod4
there were 20 players on the server,1 airstrike dropping bombs and 1 chopper flying while I was at a vantage point(a point where you get a big view of the map) and I was having 42 FPS

so what I am asking for that if there is a way to enable fullbright in every server in mw2
and If possible without any cheat engins or hacks

Have you tried to change the graphics? Run the game in high priority?
I used to have problems aswell, i tried experimenting with my graphics, fixed from 70 to ~140 FPS.