Many thanks for the replies!
I suspected you didn't need a visa for hour building, but I wasn't so sure if I still needed a tourists visa to go. The last time I was in the US ('05), I'm sure even tourists had to have a visa - that's where my confusion arised.
I must say though, I'm surprised you do not need one for the CPL since surely this is a course of study & you would be regarded as a student?
Anyhow, many thanks once again.