First of all, we had a proper meeting with the team from the PCC, and decided that, with a greatly reduced budget, a totally custom-built solution, including all desktop machines and the server, would be the only way to make it affordable. I did a little research, and came up with a specification of parts from Misco that would suit our purposes - we had almost made the order when, suddenly, a friend told me about another website where we could get a similar / better spec for a much lower price, and we went with that instead.
It's a good thing we did, as we're now opting to use Windows Home Server, as opposed to the free Ubuntu server software, which will increase the cost of the server by around 50% (~£170).
Anyway, we got all the parts for the computers delivered to the PCC, and set about building. On the first day, we spent our whole 2 hours building one machine for the reception (it'd been a while...), but the next day, we built 4 and a half in the same amount of time. By the end of the next trip, we had finished all 5 of the suite's desktop machines and had Windows 7 and Office 2010 installed on each and every one, and the trip after that, we had a built server with Ubuntu installed (which we eventually chose not to use). The PCC staff were so impressed with the performance of their new Reception machine that they requested another, which we will soon build.
With all the machines set up and working, it's time to be thinking about networking. We worked out how to crimp (stick the ends on) the Ethernet cabling which makes up the backbone of the system, and got several computers linked to each other, and worked out how we would be connecting everything (with a little help from the school's network manager). This will involve some drilling, which we can't do ourselves, so basically all we have to do for now is get Home Server installed, and see if we can get the network partially up and running, essentially by sticking everything in the switch and seeing what happens.