its happened twice now right at the start of the game when i get the varmit rifle and i have to shoot the bottles as soon as i take the first shot it crashes

You haven't told us ANYTHING, sorry. If you have a console, please go to the forum you belong in. If you have a PC, you must offer the standard diagnostic information.

http://en.wikipedia.org/wiki/System_requirements

Minimum System Requirements (VGAs corrected for Obsidian stupidity):

* Windows XP/Vista/Win7
* 1GB System RAM (XP)/ 2GB System RAM (Vista)
* 2.0 Ghz Dual Core processor
* Direct X 9.0c compliant video card with 256MB RAM
(NVIDIA 6800 "GS" or better/ ATI X1300XT or better)
{Added my note here, the X1600 Pro & up really, and
avoid both the Geforce 6800 SE, and the 6800 XT}
* 10 GBs of free hard drive space