First of all be sure to use the hotfix that was released for the betapatch, many people had more crashes than ever before running this beta wihout the hotfix.
http://forum.1cpublishing.eu/showthread.php?t=32035
Then try and play with the graphics options like mentioned above, turn them all down to start with and if that works slowly work your way up. Especially stuff like trees,shadows,roads,SSAO and texture quality are known to make lower spec pc's choke.
Even deleting the logo.wmv file from Ubisoft is known to cause problems with GPU's not going into 3d mode and might contribute to crashes as your graphics card is "idling" while having to load tons and tons of textures.