My struggles to get Windows 7 RC to install were eventually resolved with a slightly unusual solution: abandoning the 32-bit release in favour of the 64-bit package.
Having tried two additional clean installs on top of the the one I wrote about on Friday, I'd started to run out of obvious options to get the software working. The ever-helpful Jeff Alexander, who works as a technology evangelist at Microsoft Australia, couldn't offer any rational explanation as to why the install had gone so badly. However, he did suggest trying to install the 64-bit release instead, which unaccountably went much more smoothly and experienced no network issues at all.
I'm pleased that I've got the software working, but this kind of solution isn't going to help everyone -- especially users who eventually purchase an upgrade copy (we won't have free trial downloads forever) or who can't run the 64-bit option on older hardware. So I hope Microsoft puts some more work into ironing out those bugs before October. In the meantime, if you've been having RC issues and your hardware is up to it, a 64-bit install might be a useful cure.