OK, I have messed up certificates in SBS2008, my original issue was that the Exchange cert had ran out and needed renewing, so I followed a blog post with instruction on how to create a self signed cert and install it, this failed as the domain name was not included in the cert details. I then found another post which suggest running Fix Network or somesuch which then broke internet access to the network clients and the server.
So now I have a knackered server, please help.