Thanks damien551 for checking the dxdiag. Looks like you do have an 865G then. So it's strange that the driver couldn't install. Can you tell us what the exact error message was when the driver install failed? You can also try Peacenote's suggestion of going to Dell. Maybe Dell doctored the chipset and have some proprietary drivers that are different from Intel's.
I noticed another problem. The requirements for Wildlife Park 2 is 512MB of system RAM and 64MB of graphics RAM. Damien551's computer has 512MB of system RAM, but part of that RAM is shared by the video card. So, at least on paper, you didn't really make the requirements. And maybe the lack of video RAM is causing those pixel shader errors. On the other hand, MM2 would work because it only requires 256MB system RAM and 16MB graphics RAM That still doesn't explain why you cannot install the latest Intel drivers on an Intel video card though.
EDIT: As far as the Pixel Shader is concerned, Wildlife Park 2 only needs Pixel Shader 1.1, which should be supported by the Intel 865G since Intel labels it as a Directx 9.0 chip.
EDIT2: Doing some reading on Intel's site shows that the 865G does not have hardware pixel shader support (or hardware T&L), which means it must use software emulation. This also means that games which specifically check for hardware pixel shader support won't work with the 865G. Don't know if Wildlife Park 2 is one of those games.
belleh: Looks like Wildlife Zoo and Wildlife Park 2 have the same system requirements, so the answer is: probably not.