you could manage with 250-300 All res in hell with no problem i should think. depends on playstyle, if you have very good dps then resist is not so important.
In general, the most important resists for any difficulty are physical and fire. That being said, you want gear with all resist, not just a single resist. This is more for Inferno though. Hell mode isn't that big of a deal imo, and as long as you have decent vitality and dps you should do fine.
If you're playing hardcore, that's an entirely different story. For hardcore you really need to focus on all resist once you hit 60. And before that you want to stack as much armor and health as possible.
If you tell me your class, build, and general stats I can give more specific help for finishing hell and moving into inferno. Also, are you playing hardcore? I ask since you mentioned not dying.
150 - 200 is fine to clear hell. Hell, I started hardcore Inferno on my barb with 200.
Like Laurcus pointed out, get all much all resist, but your primary ones to take are fire and physical. I say this because you can, with most classes, avoid the arcane lines if you practice, and until Inferno the lightning damage isn't that amazing. Most of the time you'll be taking fire damage from mortar or molten.