AGP Aperture Size ?

I downloaded the game “Cossacks 2: Battle for Europe” and copied over the crack to the game dir and when i start the game i get this error.

So i proceeded to my BIOS and found no such option
My motherboard is Asus P5Q Pro and my graphics card is Ati Radeon HD 3870 512mb.
So how do i set the AGP Aperture Size to 256mb ?
Answer #1
this is a weird one. this site explains what the agp apeture size is
http://www.techpowerup.com/articles/overclocking/vidcard/43
the fact that it is ‘AGP’ (as in accelerated graphics port, the port that was used for graphics cards before PCI-E – nVidia 7 series and older) and the fact that ive only seen it mentioned in older articles meens that it probably isnt something thats used any more
how much ram do you have?
Answer #2
all the articles ive read are from 2003/04 so i dont think its used now ?
I have 4GB DDR2 Ram.
Answer #3
i think PCIE changed the way the video ram is addressed by the BIOS, in order to get rid of that. Do you have an older computer that you can play the game on?