Yup, Andy is spot on with his advice.
Sounds like you have a 4-port router/switch, so just plug your new desktop in there. It's fairly easy to share things in Windows. Just make sure you have File & Print Sharing installed (should be added as default) and you can share folders from each of your machines with the others (via Network Neighbourhood in Explorer).
As for scheduling software, it depends how you want to do it. One quick and dirty method may be to build yourself something in Excel and then share it (Tools, Share Workbook).