I'm in front of a big IT choice for my little office and I need some advice.

We have 5 users, 1 super user, 1 HP500 DesignJet Plotter, other 4 laser printers, 1 HP Fax/Print/Scan/Copy machine. All the clients are XP Sp3 boxes. We would like to:

1. centralize and share 90Gb of files using a Dropbox (this way we will have LAN sync of local working directories + internet backup + access our files wherever we are).
2. centralize our plotter, printers and fax machine backup all the workstations
3. share outlook calendar and tasks
4. run 24x7 saving some energy

Of course this setup It's just the first step to a more serious and creative network management of our office, so we are open to new ideas.

The budget vary from 400€ to 900€, we are not tech gurus but at least one of us is a power user close to become a geek.

I've read some articles on macminicolo about a mac mini either normal or with snow leopard server. I heard about Windows Home Server too on the lifehacker website but I'm in a sort of analysis - paralysis can You help me?