68mm x 113mm BB, that's what's normally used for triples on road style, which is only part of the equation and has absolutely no correlation with crank length.
UN54 is a shimano cartridge JIS square taper BB, so you can use sugino, older shimano or there abouts.
http://www.sheldonbrown.com/bbsize.html
I'd just take it to the shop you bought it from and ask them if they will swap out the cranks for shorter ones for you.
thanks to all for the replies. i looked at sheldon's page but really couldn't make much sense out of it tonight, i'l try another time when my mind isn't reeling from work.
I got the bike on ebay, so the shop swap isn't really an option, but i'd prolly just bring it to my LBS anyhow.
BTW i should have mentioned that i want shorter cranks partly because i have knee issues. i've read more than once that cranks too long can exacerbate knee issues, particularly anterior ones.
still happy for any help and specific recommendations!
cheers, m