I have enough memory 8 GB, Windows 7 64 bit, I7 processor, 3.4 Mhz and overclocked ATI graphics 5750 with 1 GB. Had constant CTD just after a torpedo hit. Use TDW mod(s). After uninstalling IRAI mod, everything is running smooth.
So perhaps try to run without mod(s) and reload mods one by one. maybe you are lucky and you wil find the problem.
No idea why it is the IRAI mod that is causing the problems in my mod setup.