I've been given the opportunity to quote to build a new network in an existing building.
It's to cover at least 6 PC's - I have so far only done upto 3 and have just used a statndard router as nothing complicated was necessary - but this is a bit of a different ballgame !

can anyone suggest a decent website for reference material and general recomendations, hints and tips etc

just get a 8 port switch instead of a 5 and you should be good.

so basically set up a single server pc and link everything through the hub to this

Are you interested in setting up a domain, or sticking with a workgroup?
The client-server architecture would be more expensive and the benefits are fewer with such a small network, however if the business does grow the IT infrastructure would be simple to expand.

You shouldn't have any trouble connecting all computers with a single switch. Running automated backups to a NAS or a server is a great idea.

don't know enough about domains - so would stick with workgroup.

still need some reading material though please

There ya go:

http://www.microsoft.com/windowsxp/using/networking/setup/default.mspx