Hey there again monkey_boy. It seems your (admittadly slightly amusing) comment about Powerpoint has dragged all the trolls out from their caves!
A 64-bit OS allows the OS to see all of your memory, up to 16gb. Each 32-bit program can only see 3gb, but not necessarily the same 3gb. So if you had 9gb of RAM, and three 32-bit programs, they'd still each get all they could need.
As this is for a department at work I'm even more convinced you don't need an i7 machine. You probably don't even need a Quad-core, though I would recommend one myself. The machine I linked is definitely the best option I can see on OcUK, but if you're against AMD (I know some people are) perhaps you should put together a machine yourself from Intel parts, as there doesn't seem to be a cheap Quad-core Intel available although I know they are easily enough put together!
As you don't even need a graphics card, maybe try ringing up OcUK and asking how much cheaper you could get the system without graphics cards. As you are buying three I'm sure OcUK will do everything within their power to help you.
A 32bit windows application can ONLY use up to 2G of RAM however much the OS has available unless the 32bit app is PAE aware (which is very rare). This will be the case if the application is run on a 64bit version of windows as well.