Need advice/reccomendations

[hoemee]

I need some advice and recommendations - this may be long so please bear with me. I am not sure what I need but I know you folks can get me on the right track.
I am involved with a non-profit organization and need to set up a computer system for our organization, which I think is either a network or server - I am not sure. I have built several computers and am somewhat of a tweaker, but this is beyond my knowledge.
OK - I know I need at least four computers. I need one for the secretary, treasurer, president and banquet coordinator - possibly two more. We have a 1000+ member organization that needs to track, store and update membership information. We also have a business of banquet hall and lounge and two bars. I would like to have computerized cash registers to store all sales and money related transaction.
Software requirements - we would like to upgrade to Windows XP, and run Microsoft Office applications. We have just upgraded to a Peachtree acconting system.

Now, I will build these computers for them and I know we don't need blazing speed and graphics, but we will be generating a lot of reports and data for tracking.

Where do I start?

Thank you all in adavance,

Steven