i can't honestly remember which programs i've tried in the past but, if i remember correctly, they don't quite do the full job that is required.
the problem lies in the edges of the print and more importantly, how you join them all back together.
if you don't mind having 'rough' edges and obvious overcuts and undercuts in your final joined poster then there's nothing to worry about. or, perhaps, you are an eagle eye cutter that can cut the perfect edge so that you don't stray into the part that contains the print and nor do you stray away from it thereby leaving an obvious white sliver.
maybe my memory doesn't serve me well and there is a program i tried that did a slight 'overprint' so that you don't need a qualified surgeon to perform the cutting out. i do remember just using ms publisher in the end as that allowed me to adjust overprint borders how i wanted them.
now that my brain is getting warmed up i think 'poster printery' probably had the ability????