Jon Luskin- I work on these older Cannondale ST's a bunch and come across this problem quite often. Short version is an older crank like the one you had requires a wider BB- and often to get it out far enough on the drive side the BB itself is asymmetrical by 3mm or more (e.g. the drive side sticks out farther than the non-drive side).

Modern cranks are offset within the spider and do not require as much offset or as wide a BB. So the crank you bought is not good for that bike unless you match it with the correct FD and BB and the suggestions already given are solid. If you want to continue using the BB on the bike, find an equivalent vintage triple crankset that will work with your FD. If you're having trouble finding one, PM me as I have several good ones in stock and I'm pretty sure one or two of them have the 28 small ring.

EddyR- I have one of those Suntour BB's and they actually use a pair of easily obtained sealed bearings (I think 30 X 17). If yours was dry, the new grease will only hide the problems for a short time, since dry = very bad. A replacement isn't needed unless the spindle is worn out, just buy new bearings.