I just came across your message posted on rootsweb back in Sept 2006. Like you i am trying to trace my Hiam ancestors.
I was born in Outwell,which is a very short distance from Upwell,most of my descendants came from around this area,my father was born in a small village called Christchurch a few miles from Outwell,& his grandfather came from a town called Manea,also in the same area. I know there were some Hiam's in the Upwell-outwell area during the 1600's & i am fairly sure we must be related to them,I'm just going through the process of of trying to prove it.
I migrated to Australia with my family in the 1950's,but i still go back to England fairly often.