Interesting. Info from Nasa suggests that nicads should be stored at around 0 degrees, and in a discharged state. Each cell in a pack should be discharged, then shorted. It doesn't work to short the entire pack, since some cells will then become reverse charged. Because we won't be opening up our drill packs to do this, the next best option is to fully charge the battery, then discharge it partially, then keep it cool. Refrigeration is not recommended basically because of the moisture present. Clean the battery contacts, wipe the battery clean and dry, then put in a ziplok bag to seal moisture out. Safe to store down to -20C, recommended to store at about 0.
This is a condensation of info from a few different internet sites, stuff which seemed to generally be in agreement. What is also recommended is if the battery has been stored for more than a couple of weeks, that it should be given a full recharge/discharge/recharge cycle, starting with a reduced charge rate. After a partial charge at the reduced rate, a full speed charge can be done. Most of us won't have the capability to do this, and will have to rely on the charger that came with the tool to do the job. Probably the best thing to do after storage for some time is to try the battery in the tool, running it down if there's charge left, then recharge fully. Follow with a full discharge, then recharge again. The full discharge should be done by using the tool until the battery goes dead, preferably within the day. Recharge as soon as the battery has cooled, if it has become warm or hot. Using up the full charge over a short period of time helps to keep the battery able to accept and deliver it's full capacity.
A repeated full discharge/charge cycle is sometimes recommended so you can know how much power can be drawn before it goes dead. Not too important for a drill, more so for an RC model, but also good if the battery is going to be unused again for awhile.