Should have done some investigation before raising the issue here, but since I did, I should probably fill you in on the outcome...
Decided to remove some questions about machine setup, so I went to the top rated machine I have - Core2Duo, 2GB RAM and 2TB HDD. It has XP SP3 and IE8 with latest updates.
Online viewing (20 transactions at a time) of a whole year's data was delivered in about 20 sec. No way would it download, though. Would go off thinking for a minute or so and then the page would die with a page no longer valid message (I think it was). Worked fine, albeit a bit slow I thought, with six months data, though.
So, note entirely sure what the original problem was, but the data is downloaded.
As for the bookkeeping side of their business, we have been trying to find the time to find the best product for their needs, the time to set it up and the time to load the data - but it seems we are hard pushed to find the time to scratch ourselves.
I'll put up a thread in the Round Table board on this and invite your contributions there. I will give some more detail on what we're after, too.