Living just a few miles from both places I might be able to help you.
First 's Hertogenbosch is the older name for Den Bosch, just modern spelling. 's Hertogenbosch means woods for the Dukes. The city center is very nice, not only for shopping, but also for the history of it. Don't forget to walk in the Cathedral of St Jan.
The public transport in Holland isn't that widely spread. There's no train station in Heusden and the bus only stops outside the old city wall, so you'll have to walk inside the city which is a lovely walk of about 10 minutes. You'll see the dike or earthen wall to protect the old village against water and former enemies (from the Middle Ages). From the Central Station in Den Bosch you need to take bus 135 and just ask the driver to call you for the stop near Heusden Vesting. It will take about half an hour. The bus only goes one time every hour at 25 minutes past the hour.
Another option is to take a boat tour from Den Bosch over the river to Heusden. It only sails from june untill oktober on teusday, thursday, saturday and sunday. You'll enjoy the Dutch river Maas and go through a sluice. A two hour stop in Heusden will be enough to see the village, it's very small. (see http://www.rederijwolthuis.nl/heusden-dagtocht)
The 9292.nl site Pala mentioned is the public transport planner for Holland. If you use it Den Bosch = 's Hertogenbosch. Heusden should be Heusden gem Heusden. Nothing else or you'll end up in another village !
Have fun planning your trip, I'm sure you'll very much love the area if you enjoy the Middle ages and Gothic buildings. If you need any help don't hesitate to ask...I'm a professional in tourism :).