Do I need a different bottom bracket? I have a road bike that has a triple chainwheel setup (48x38x28)in which the chainwheels are not replaceable.  (Made by SunTour)  The middle chainwheel has broken a tooth so the whole thing needs to be replaced.  What a waste...

Anyway, I want to upgrade to a Shimano M361 crankset with the same tooth size chainwheels (48x38x28) that has the nice benefit of having replaceable chainwheels.  

I have a Shimano JIS sealed bottom bracket; 117.5 spline size on the bike right now.

My question is do I have to replace the bottom bracket with a different size or will the existing one be fine?

The three bike shops here in town were no help.  One tells me it will work, one says it will not, and the last wasn't sure.  

Thanks for your help!
The datasheet for the crankset says it calls for a 123 mm spindle length. This would mean that your crankset would sit about a half centimeter further out than the existing one if you use the Shimano recommended bottom bracket, which will affect the chainline. 

I'd go for trying it out as is -- it will probably work. If the shifting is fine, and the chain isn't jumping or derailing when its not supposed to, you're good to go. If it is having problems after adjustments, get a new bottom bracket.