Got the email wink

Bert's advice is pretty good with a few minor adjustments. Server 2012/2012R2 Standard would be a good investment.

There's a few possible layouts:

It depends on your requirements and level of separation. I'm not completely clear on the extent of separation. Sharing staff, etc.

Possible scenarios:
1. Shared Access to Files/Programs but only Separate Amazing Charts. Users will share the same base of files shares, printers, etc. You could control folder permissions to ensure he can't see your files and you can't see his.
2. Two completely separate and isolated networks. Makes sense in a limited circumstance. If the same staff are cleared for both practices and staff is shared, then this seems a bit unnecessary.

Scenario 1 Layout:
Server 2012 R2 (Hyper V Host)
->Server 2012 Instance 1 (Other Physician's AC/Database and Remote Desktop Services)
This would host the Amazing Charts/SQL Database in addition to providing AC as a Remote Desktop Application or RemoteApp. Restrict users heavily so they can only execute Amazing Charts and nothing else.

->Server 2012 Instance 2 (Downgrade to 2012 Essentials R2)
This would host your Amazing Charts in addition to being a domain controller. Since you already have all Windows 7 Pro, you get good stuff like Folder Redirection, Network Backup, Group Policy etc.

Experience:
Users will have all the same stuff as before. Except the ability to run 2 copies of Amazing Charts. One will be running locally off Server Instance 2 using Windows 7. The other will run remotely off server instance 1 using RD App. This assumes you want to keep it easy on your staff and simply want two copies of AC on the same computer while leaving all current files and settings in-tact.