I tried the jump on mine and it works every time. I ran and jumped to the open part in the middle. Nothing fancy....no running at an angle. My game setting is default to run. However, this is a known problem for a lot of people. If nothing you try works, I would uninstall the game, then, delete the Infernal Machine folder in the LucasArts folder (in Program Files). Do that AFTER you Uninstall the game. Then Install the game AND the patch before playing the game. If you still have the problem after all that, I would suspect that your computer or video card is below minimum system requirements. Go to www.lucasarts.com
and click on Support, then Troubleshooting Infernal Machine for information. Good luck
ps: when installing the game, if you can spare the hard drive space, the complete install is better because it loads much faster.