You can't tweak the config file for Assassins Creed 2, like you can do with AC1, sorry.
I tried this and it didn't work, believe me. You're being held down by your PC. It doesn't meet the minimum requirements to run the game.
SUPPORTED OS: Windows XP (32-64 bits) / Windows Vista (32-64 bits) / Windows 7 (32-64 bits)
Processor: Intel Core 2 Duo 1.8 GHz or AMD Athlon X2 64 2.4 GHz
RAM: 1.5 GB Windows XP / 2 GB Windows Vista - Windows 7
Video Card: 256 MB DirectX 9.0-compliant card with Shader Model 3.0 or higher
Sound Card: DirectX 9.0 -compliant sound card
DirectX Version: DirectX 9.0
DVD-ROM: DVD-ROM dual-layer drive
Hard Drive Space: 8 GB
Peripherals Supported: Keyboard, mouse, optional controller
* This product does not support Windows 98/ME/2000/NT
Processor: Intel Core 2 Duo E6700 2.6 GHz or AMD Athlon 64 X2 6000+ or better
Video Card: GeForce 8800 GT or ATI Radeon HD 4700 or better
Sound: 5.1 sound card
Peripherals: Keyboard, mouse, joystick optional (Xbox 360 Controller for Windows recommended)