To mine most crypto-currencies you'd need a good graphics card, preferably AMD than nVidia. Graphics chips integrated with the mother-board are typically bad for this, if they can be used at all.
There are some cryptocurrencies you do can mine with CPU only, like Protoshares, Quarkcoin, Primecoin and a few others. To avoid affecting the normal usage of a computer, mining program can run with a very low priority so it's only running when computer's not really used.
However, mining on a laptop is strongly discouraged for they're typically not designed to be run with their processors at 100% the whole time, so you're going to wear down the components earlier due to overheating - capacitors, battery, even hard-drive or microprocessor could die earlier because of that (e.g. Apple Airs wear down very fast if you put them to mine, a friend of mine experienced it).
If you can somehow ensure they'll have VERY good ventilation, or if you limit the mining to 4 or 5 hours a day, with several "rest" hours between each, you might make some money off them. But then, you ought to measure carefully the cost of the extra power they eat (plus the extra refrigeration's consumption) vs. what they would take if idle, vs. what you earn after a while - it might be profitable, or it might not.