The pipes to reach the top area are glitched so it's not possible to get up there without turning on fly.
Here's what my pipes look like:
Here is what they should look like (as seen on walkthrough video):
Shader model: 2.0
Hardware physics: on
Advanced Physx effects: off
ATI Mobility Radeon HD 5470
Driver Version: 8.680.0.0
I'm not worried since I can use the fly workaround but I wanted to let you know anyway