You could always try SH2, but I'm guessing your PC would run SH3, albeit not with all the graphics on full throttle. If you want to simulate as many of the on-board systems of a sub, then DW may very well be a better choice though. DW will run on just about any computer because it's not an eye-candy fest. If you like playing with analysing signals and stuff like that, DW is far more likely to float your boat, plus the 'Akula' is very groovy. Warning: DW has a steep learning curve, expect a week of frustration, as it is very 'in-depth'!
Chock