I really need to hammer out some radiation rules - I came up with some that really, really made me hate them even before trying them out. (A Fort save every round of exposure, a successful save halving the doses for the round, with ability damage being inflicted at 200, 400, 600, and 800 rads - automatic death at 1000 rads. The real number crunching fun coming in when rad resistance (Rad-X, feats, etc) removing a percentage before the save... 'Let's see, six rads per round, a 20% resistance, call it four rads, make a save - oh look, you gained 2 rads, only 198 rads to go before it starts having an effect....) Blaaaaarrrrgggghhh!
The kind of thing a computer excels at, but that sucks at the table.
I am now considering a threshold system, with rad resistance increasing the threshold, and a save delaying the effects of crossing the threshold. So, accumulate rads until 200, or 240 if you have a 20% rad resistance, then a save has to be made every ten minutes and each time you accumulate more rads.
Accumulating rads is important, because even eating and drinking in the Wastes adds to your radiation.
Going with the numbers from Fallout radiation damage, modified for Spycraft, and made a trifle nastier:
200 Rads: -1 Con
400 Rads: -1 Str, - 1 Con
600 Rads: -1 Dex, -1 Str, -1 Con (Permanent.)
800 Rads: -1 Wis, -1 Dex, -1 Str, -1 Con (Permanent.)
1,000 Rads: You probably welcome death by now....
Saves must be made every 10 minutes, and can continue doing damage unless the rad level is dropped - so at 400 rads every 10 minutes you risk losing another 1 Str and 1 Con with a failed save.
Rad resistance may be paired with a feat that can lead to ghoulification, and will definitely be in a background that can do so. If you reach 1,000 rads, or remain at 400+ rads for long enough then you.
The system still needs to be beaten on with a hammer.
The Auld Grump - this is not trying for a realistic system, but rather trying to replicate some of the feel of radiation in Fallout 3.
*EDIT* Just food and drink probably adds another 5-10 rads every day.