I do this for a living, so here's a few more questions (I see some were asked by PCM2 already):
How many buildings are there on the property? How tall is each one? What is the layout (facing each other, central courtyard, one long line)? What is the construction material of the exterior of the buildings? The interior (between rooms)?
Is there a central telephone room that all the buildings link into? Have you run a line tone to make sure?
Check each room to see how many telephone pairs are going in. If there is more than one pair and the n+1 pairs are not in use, then you can throw in and mount a wireless modem in each room. There are vendors that make mounts that are tamper-resistant. The trick is to find out how much penetration the wifi signal from that modem is going to get between each room. Buy one modem, get access to a room, and to all the rooms adjacent (above, below, sides, and across the hall) to see what kind of coverage you can get. Download inSSIDER to help with this analysis.
From this testing you'll be able to determine what kind of signal you're getting in the adjacent rooms, and thereby determine what layout of modems you need.
Get a DSLAM on the property, and get your system up and running.
How you chose to manage the back end is up to you; we use RADIUS. However, since you're managing a single location, you could probably do it with an HP Procurve MSM 710 or even an MSM 313. This will track user logins and sessions independent of any wireless access point that you set up.